# Infinispan Guide to Cross-Site Replication

Find out how Infinispan performs cross-site replication so you can get optimal performance and avoid issues. Learn how to configure Infinispan to back up data to remote clusters. Follow procedures to transfer state from one cluster to another, take sites offline, and so on.

## 1. Infinispan Cross-Site Replication

Cross-site replication allows you to back up data from one Infinispan cluster to another. Learn the concepts to understand how Infinispan cross-site replication works before you configure your clusters.

### 1.1. Cross-Site Replication

Infinispan clusters running in different locations can discover and communicate with each other.

Sites are typically data centers in various geographic locations. Cross-site replication bridges Infinispan clusters in sites to form global clusters, as in the following diagram:

LON is a datacenter in London, England.
NYC is a datacenter in New York City, USA.

| Infinispan can form global clusters across two or more sites. For example, configure a third Infinispan cluster running in San Francisco, SFO, as backup location for LON and NYC.

#### 1.1.1. Site Masters

Site masters are the nodes in Infinispan clusters that are responsible for sending and receiving requests from backup locations.

If a node is not a site master, it must forward backup requests to a local site master. Only site masters can send requests to backup locations.

For optimal performance, you should configure all nodes as site masters. This increases the speed of backup requests because each node in the cluster can backup to remote sites directly without having to forward backup requests to site masters.

| Diagrams in this document illustrate Infinispan clusters with one site master because this is the default for the JGroups RELAY2 protocol. Likewise, a single site master is easier to illustrate because each site master in a cluster communicates with each site master in the remote cluster.

### 1.2. Adding Backups to Caches

Name remote sites as backup locations in your cache definitions.

For example, the following diagram shows three caches, "customers", "eu-orders", and "us-orders":

- In LON, "customers" names NYC as a backup location.

- In NYC, "customers" names LON as a backup location.

- "eu-orders" and "us-orders" do not have backups and are local to the respective cluster.

### 1.3. Backup strategies

Infinispan replicates data between clusters at the same time that writes to caches occur. For example, if a client writes "k1" to LON, Infinispan backs up "k1" to NYC at the same time.

To back up data to a different cluster, Infinispan can use either a synchronous or asynchronous strategy.

#### Synchronous strategy

When Infinispan replicates data to backup locations, it writes to the cache on the local cluster and the cache on the remote cluster concurrently. With the synchronous strategy, Infinispan waits for both write operations to complete before returning.

You can control how Infinispan handles writes to the cache on the local cluster if backup operations fail. Infinispan can do the following:

- Ignore the failed backup and silently continue the write to the local cluster.

- Log a warning message or throw an exception and continue the write to the local cluster.

- Handle failed backup operations with custom logic.

Synchronous backups also support two-phase commits with caches that participate in optimistic transactions. The first phase of the backup acquires a lock. The second phase commits the modification.

| Two-phase commit with cross-site replication has a significant performance impact because it requires two round-trips across the network.

#### Asynchronous strategy

When Infinispan replicates data to backup locations, it does not wait until the operation completes before writing to the local cache.

Asynchronous backup operations and writes to the local cache are independent of each other. If backup operations fail, write operations to the local cache continue and no exceptions occur. When this happens Infinispan also retries the write operation until the remote cluster disconnects from the cross-site view.

#### Synchronous vs asynchronous backups

Synchronous backups offer the strongest guarantee of data consistency across sites. If `strategy=sync`, when `cache.put()` calls return you know the value is up to date in the local cache and in the backup locations.

The trade-off for this consistency is performance. Synchronous backups have much greater latency in comparison to asynchronous backups.

Asynchronous backups, on the other hand, do not add latency to client requests so they have no performance impact. However, if `strategy=async`, when `cache.put()` calls return you cannot be sure of that the value in the backup location is the same as in the local cache.

### 1.4. Automatically Taking Backups Offline

You can configure backup locations to go offline automatically when the remote sites become unavailable. This prevents Infinispan nodes from continuously attempting to replicate data to offline backup locations, which results in error messages and consumes resources.

Timeout for backup operations

Backup configurations include timeout values for operations to replicate data. If operations do not complete before the timeout occurs, Infinispan records them as failures.

    <!-- Operations to replicate data to NYC are recorded as failures if they do not complete after 10 seconds. -->
    <backup site="NYC" strategy="ASYNC" timeout="10000">
            <!-- Configuration for backup locations goes here. -->
    </backup>

Number of failures

You can specify the number of consecutive failures that can occur before backup locations go offline.

For example, the following configuration for NYC sets five as the number of failed operations before it goes offline:

    <!-- If a cluster attempts to replicate data to NYC and five consecutive operations fail, NYC automatically goes offline. -->
    <backup site="NYC" strategy="ASYNC" timeout="10000">
      <take-offline after-failures="5"/>
    </backup>

Time to wait

You can also specify how long to wait before taking sites offline when backup operations fail. If a backup request succeeds before the wait time runs out, Infinispan does not take the site offline.

    <!-- If a cluster attempts to replicate data to NYC and there are more than five consecutive failures and 15 seconds elapse after the first failed operation, NYC automatically goes offline. -->
    <backup site="NYC" strategy="ASYNC" timeout="10000">
      <take-offline after-failures="5"
                    min-wait="15000"/>
    </backup>

| Set a negative or zero value for the `after-failures` attribute if you want to use only a minimum time to wait to take sites offline.
    <take-offline after-failures="-1" min-wait="10000"/>

### 1.5. State Transfer

State transfer is an administrative operation that synchronizes data between sites.

For example, LON goes offline and NYC starts handling client requests. When you bring LON back online, the Infinispan cluster in LON does not have the same data as the cluster in NYC.

To ensure the data is consistent between LON and NYC, you can push state from NYC to LON.

- State transfer is bidirectional. For example, you can push state from NYC to LON or from LON to NYC.

- Pushing state to offline sites brings them back online.

- State transfer overwrites only data that exists on both sites, the originating site and the receiving site. Infinispan does not delete data.

  For example, "k2" exists on LON and NYC. "k2" is removed from NYC while LON is offline. When you bring LON back online, "k2" still exists at that location. If you push state from NYC to LON, the transfer does not affect "k2" on LON.

| To ensure contents of the cache are identical after state transfer, remove all data from the cache on the receiving site before pushing state. Use the `clear()` method or the `clearcache` command from the CLI.

- State transfer does not overwrite updates to data that occur after you initiate the push.

  For example, "k1,v1" exists on LON and NYC. LON goes offline so you push state transfer to LON from NYC, which brings LON back online. Before state transfer completes, a client puts "k1,v2" on LON.

  In this case the state transfer from NYC does not overwrite "k1,v2" because that modification happened after you initiated the push.

#### 1.5.1. Automatic State Transfer

By default you must manually perform cross-site state transfer operations with the CLI or via JMX or REST.

However, when using the asynchronous backup strategy, Infinispan can automatically perform cross-site state transfer operations. When it detects that a backup location has come back online, and the network connection is stable, Infinispan initiates bi-directional state transfer between backup locations. For example, Infinispan simultaneously transfers state from LON to NYC and NYC to LON.

| To avoid temporary network disconnects triggering state transfer operations, there are two conditions that backup locations must meet to go offline. The status of a backup location must be offline and it must not be included in the cross-site view with JGroups RELAY2.

Reference

- org.infinispan.Cache.clear()

- Clearing Caches with the CLI

- Clearing Caches with the REST API

- Configure Cross-Site State Transfer

### 1.6. Client Connections Across Sites

Clients can write to Infinispan clusters in either an Active/Passive or Active/Active configuration.

#### Active/Passive

The following diagram illustrates Active/Passive where Infinispan handles client requests from one site only:

In the preceding image:

1. Client connects to the Infinispan cluster at LON.

2. Client writes "k1" to the cache.

3. The site master at LON, "n1", sends the request to replicate "k1" to the site master at NYC, "nA".

With Active/Passive, NYC provides data redundancy. If the Infinispan cluster at LON goes offline for any reason, clients can start sending requests to NYC. When you bring LON back online you can synchronize data with NYC and then switch clients back to LON.

#### Active/Active

The following diagram illustrates Active/Active where Infinispan handles client requests at two sites:

In the preceding image:

1. Client A connects to the Infinispan cluster at LON.

2. Client A writes "k1" to the cache.

3. Client B connects to the Infinispan cluster at NYC.

4. Client B writes "k2" to the cache.

5. Site masters at LON and NYC send requests so that "k1" is replicated to NYC and "k2" is replicated to LON.

With Active/Active both NYC and LON replicate data to remote caches while handling client requests. If either NYC or LON go offline, clients can start sending requests to the online site. You can then bring offline sites back online, push state to synchronize data, and switch clients as required.

#### Backup strategies

| With an Active/Active configuration, you should always use an asynchronous backup strategy (`strategy=async`).

If multiple clients attempt to write to the same entry concurrently, and the backup strategy is synchronous (`strategy=sync`), then deadlocks occur. However you can use the synchronous backup strategy with an Active/Passive configuration if both sites access different data sets, in which case there is no risk of deadlocks from concurrent writes.

#### 1.6.1. Concurrent Writes and Conflicting Entries

Conflicting entries can occur with Active/Active site configurations if clients write to the same entries at the same time but at different sites.

For example, client A writes to "k1" in LON at the same time that client B writes to "k1" in NYC. In this case, "k1" has a different value in LON than in NYC. After replication occurs, there is no guarantee which value for "k1" exists at which site.

To ensure data consistency, Infinispan uses a vector clock algorithm to detect conflicting entries during backup operations, as in the following illustration:

                LON       NYC

    k1=(n/a)    0,0       0,0

    k1=2        1,0  -->  1,0   k1=2

    k1=3        1,1  <--  1,1   k1=3

    k1=5        2,1       1,2   k1=8

                     -->  2,1 (conflict)
    (conflict)  1,2  <--

Vector clocks are timestamp metadata that increment with each write to an entry. In the preceding example, `0,0` represents the initial value for the vector clock on "k1".

A client puts "k1=2" in LON and the vector clock is `1,0`, which Infinispan replicates to NYC. A client then puts "k1=3" in NYC and the vector clock updates to `1,1`, which Infinispan replicates to LON.

However if a client puts "k1=5" in LON at the same time that a client puts "k1=8" in NYC, Infinispan detects a conflicting entry because the vector value for "k1" is not strictly greater or less between LON and NYC.

When it finds conflicting entries, Infinispan uses the Java `compareTo(String anotherString)` method to compare site names. To determine which key takes priority, Infinispan selects the site name that is lexicographically less than the other. Keys from a site named AAA take priority over keys from a site named AAB and so on.

Following the same example, to resolve the conflict for "k1", Infinispan uses the value for "k1" that originates from LON. This results in "k1=5" in both LON and NYC after Infinispan resolves the conflict and replicates the value.

| Prepend site names with numbers as a simple way to represent the order of priority for resolving conflicting entries; for example, 1LON and 2NYC.

| Infinispan performs conflict resolution with the asynchronous backup strategy (`strategy=async`) only. However, you should not use the synchronous backup strategy with an Active/Active configuration because concurrent writes result in deadlocks.

##### Conflict resolution algorithms

Infinispan provides different algorithms for resolving conflicts in addition to an `XSiteEntryMergePolicy` SPI that lets you implement custom conflict resolution strategies.

Apart from the default conflict resolution strategy, which uses lexicographical comparison, you can use Infinispan conflict resolution algorithms to:

- Always remove conflicting entries.

- Keep write operations when write/remove conflicts occur.

- Remove entries when write/remove conflicts occur.

Find all available algorithms and their descriptions in the `org.infinispan.xsite.spi.XSiteMergePolicy` enum.

Additional resources

- java.lang.String#compareTo()

- org.infinispan.xsite.spi.XSiteMergePolicy

- org.infinispan.xsite.spi.XSiteEntryMergePolicy

- Customizing the Conflict Resolution Strategy

### 1.7. Expiration with Cross-Site Replication

Expiration removes cache entries based on time. Infinispan provides two ways to configure expiration for entries:

`lifespan`

  Sets the maximum amount of time that entries can exist.
  When you set `lifespan` with cross-site replication, Infinispan clusters expire entries independently of remote sites.

`max-idle`

  Specifies how long entries can exist based on read or write operations in a given time period.
  When you set a `max-idle` with cross-site replication, Infinispan clusters send touch commands to coordinate idle timeout values with remote sites.

| Using maximum idle expiration in cross-site deployments can impact performance because the additional processing to keep `max-idle` values synchronized means some operations take longer to complete.

## 2. Configuring Infinispan for Cross-Site Replication

Configuring Infinispan to replicate data across sites, you first set up cluster transport so Infinispan clusters can discover each other and site masters can communicate. You then add backup locations to cache definitions in your Infinispan configuration.

### 2.1. Configuring Cluster Transport for Cross-Site Replication

Add JGroups RELAY2 to your transport layer so that Infinispan clusters can communicate with backup locations.

Procedure

1. Open `infinispan.xml` for editing.

2. Add the RELAY2 protocol to a JGroups stack.

3. Configure Infinispan cluster transport to use the stack.

       <infinispan>
         <jgroups>
           <!-- Extends the default UDP stack. -->
           <stack name="xsite" extends="udp">
             <!-- Adds RELAY2 for cross-site replication. -->
             <!-- Names the local site as LON. -->
             <!-- Specifies 1000 nodes as the maximum number of site masters. -->
             <relay.RELAY2 site="LON" xmlns="urn:org:jgroups" max_site_masters="1000"/>
             <!-- Uses the default TCP stack for inter-cluster communication. -->
             <!-- Names all sites that act as backup locations. -->
             <remote-sites default-stack="tcp">
                <remote-site name="LON"/>
                <remote-site name="NYC"/>
             </remote-sites>
           </stack>
         </jgroups>
         <cache-container name="default" statistics="true">
           <!-- Use the "xsite" stack for cluster transport. -->
           <transport cluster="${cluster.name}" stack="xsite"/>
         </cache-container>
       </infinispan>

4. Save and close `infinispan.xml`.

Reference

- JGroups RELAY2 Stacks

- Infinispan Configuration Schema

#### 2.1.1. JGroups RELAY2 Stacks

Infinispan clusters use JGroups RELAY2 for inter-cluster discovery and communication.

    <jgroups>
       <!-- Uses the default JGroups UDP stack for intra-cluster traffic. -->
       <stack name="xsite" extends="udp">
          <!-- Adds RELAY2 to the stack for inter-cluster transport. -->
          <!-- Names the local site. Data in caches from the local site is replicated to backup locations. -->
          <!-- Configures a maximum of 1000 site masters for the local cluster. -->
          <relay.RELAY2 xmlns="urn:org:jgroups"
                        site="LON"
                        max_site_masters="1000"/>
          <!-- Specifies all site names and uses the default JGroups TCP stack for inter-cluster transport. -->
          <remote-sites default-stack="tcp">
             <!-- Names all sites that participate in cross-site replication. -->
             <remote-site name="LON"/>
             <remote-site name="NYC"/>
          </remote-sites>
       </stack>
    </jgroups>

| Set `max_site_masters` >= the number of nodes in the Infinispan cluster for optimal performance with backup requests.

#### 2.1.2. Custom JGroups RELAY2 Stacks

The following configuration adds a custom RELAY2 stack that extends the default TCP stack:

    <jgroups>
      <!-- Uses TCPPING instead of MPING for discovery. -->
       <stack name="relay-global" extends="tcp">
         <MPING stack.combine="REMOVE"/>
         <TCPPING initial_hosts="192.0.2.0[7800]"
                  stack.combine="INSERT_AFTER"
                  stack.position="TCP"/>
       </stack>
       <!-- Extends the default UDP stack with RELAY2. -->
       <!-- Specifies RELAY2 properties. -->
       <stack name="xsite" extends="udp">
          <relay.RELAY2 site="LON" xmlns="urn:org:jgroups"
                        max_site_masters="10"
                        can_become_site_master="true"/>
          <remote-sites default-stack="relay-global">
             <remote-site name="LON"/>
             <remote-site name="NYC"/>
          </remote-sites>
       </stack>
    </jgroups>

You can also reference externally defined JGroups stack files, for example:

    <infinispan>
      <jgroups>
         <stack-file name="relay-global" path="jgroups-relay.xml"/>
      </jgroups>
      <cache-container default-cache="replicatedCache">
        <transport stack="relay-global" />
        <replicated-cache name="replicatedCache"/>
      </cache-container>
    </infinispan>

Where `jgroups-relay.xml` references a JGroups stack file such as:

    <config xmlns="urn:org:jgroups"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="urn:org:jgroups http://www.jgroups.org/schema/jgroups-4.1.xsd">

        <!-- Use TCP for inter-cluster transport. -->
        <TCP bind_addr="127.0.0.1"
             bind_port="7200"
             port_range="30"

             thread_pool.min_threads="0"
             thread_pool.max_threads="8"
             thread_pool.keep_alive_time="5000"
        />

        <!-- Use TCPPING for inter-cluster discovery. -->
        <TCPPING timeout="3000"
                 initial_hosts="127.0.0.1[7200]"
                 port_range="3"
                 ergonomics="false"/>

        <!-- Provide other JGroups stack configuration as required. -->
    </config>

Reference

- Setting Up Infinispan Clusters

- JGroups RELAY2

- Relaying between multiple sites (RELAY2)

### 2.2. Adding Backup Locations to Caches

Specify the names of remote sites so Infinispan can back up data to those locations.

Procedure

1. Add the `backups` element to your cache definition.

2. Specify the name of each remote site with the `backup` element.

   As an example, in the LON configuration, specify NYC as the remote site.

3. Repeat the preceding steps so that each site is a backup for all other sites. For example, you cannot add LON as a backup for NYC without adding NYC as a backup for LON.

| Cache configurations can be different across sites and use different backup strategies. Infinispan replicates data based on cache names.

Example "customers" configuration in LON

    <replicated-cache name="customers">
      <backups>
        <backup site="NYC" strategy="ASYNC" />
      </backups>
    </replicated-cache>

Example "customers" configuration in NYC

    <distributed-cache name="customers">
      <backups>
        <backup site="LON" strategy="SYNC" />
      </backups>
    </distributed-cache>

Reference

- Infinispan Configuration Schema

### 2.3. Backing Up to Caches with Different Names

By default, Infinispan replicates data between caches that have the same name.

Procedure

- Use `backup-for` to replicate data from a remote site into a cache with a different name on the local site.

For example, the following configuration backs up the "customers" cache on LON to the "eu-customers" cache on NYC.

    <distributed-cache name="eu-customers">
      <backups>
        <backup site="LON" strategy="SYNC" />
      </backups>
      <backup-for remote-cache="customers" remote-site="LON" />
    </distributed-cache>

### 2.4. Configuring Cross-Site State Transfer

Change cross-site state transfer settings to optimize performance and specify whether operations happen manually or automatically.

Procedure

- Use `<state-transfer>` to configure state transfer operations.

For example, the following configuration automatically performs cross-site state transfer with custom settings:

    <distributed-cache name="eu-customers">
       <backups>
          <backup site="LON" strategy="ASYNC">
             <state-transfer chunk-size="64"
                             timeout="30000"
                             max-retries="30"
                             wait-time="2000"
                             mode="AUTO"/>
          </backup>
       </backups>
    </distributed-cache>

### 2.5. Customizing the Conflict Resolution Algorithm

Configure Infinispan to use a different algorithm to resolve conflicting entries between backup locations.

Procedure

1. Open your Infinispan configuration for editing.

2. Specify one of the Infinispan algorithms or a custom implementation with the `merge-policy` attribute for the `backups` element.

Using Infinispan algorithms

Find all Infinispan algorithms and their descriptions in the `org.infinispan.xsite.spi.XSiteMergePolicy` enum.

The following example configuration uses the `ALWAYS_REMOVE` algorithm that deletes conflicting entries from both sites:

    <distributed-cache name="eu-customers">
       <backups merge-policy="ALWAYS_REMOVE">
          <backup site="LON" strategy="ASYNC"/>
       </backups>
    </distributed-cache>

Using custom implementations

1. Create a custom `XSiteEntryMergePolicy` implementation.

       public interface XSiteEntryMergePolicy<K, V> {
          CompletionStage<SiteEntry<V>> merge(K key, SiteEntry<V> localEntry, SiteEntry<V> remoteEntry);
       }

2. Specify the fully qualified class name as the value of the `merge-policy` attribute, as in the following example:

       <distributed-cache name="eu-customers">
          <backups merge-policy="org.mycompany.MyCustomXSiteEntryMergePolicy">
             <backup site="LON" strategy="ASYNC"/>
          </backups>
       </distributed-cache>

Additional resources

- org.infinispan.xsite.spi.XSiteEntryMergePolicy

- org.infinispan.xsite.spi.XSiteMergePolicy

- org.infinispan.xsite.spi.SiteEntry

- Infinispan Configuration Schema

### 2.6. Verifying Cross-Site Views

After you configure Infinispan for cross-site replication, you should verify that Infinispan clusters successfully form cross-site views.

Procedure

- Check log messages for `ISPN000439: Received new x-site view` messages.

For example, if the Infinispan cluster in LON has formed a cross-site view with the Infinispan cluster in NYC, it provides the following messages:

    INFO  [org.infinispan.XSITE] (jgroups-5,${server.hostname}) ISPN000439: Received new x-site view: [NYC]
    INFO  [org.infinispan.XSITE] (jgroups-7,${server.hostname}) ISPN000439: Received new x-site view: [NYC, LON]

### 2.7. Configuring Hot Rod Clients for Cross-Site Replication

Configure Hot Rod clients to use Infinispan clusters at different sites.

`hotrod-client.properties`

    # Servers at the active site
    infinispan.client.hotrod.server_list = LON_host1:11222,LON_host2:11222,LON_host3:11222

    # Servers at the backup site
    infinispan.client.hotrod.cluster.NYC = NYC_hostA:11222,NYC_hostB:11222,NYC_hostC:11222,NYC_hostD:11222

`ConfigurationBuilder`

    ConfigurationBuilder builder = new ConfigurationBuilder();
    builder.addServers("LON_host1:11222;LON_host2:11222;LON_host3:11222")
           .addCluster("NYC")
           .addClusterNodes("NYC_hostA:11222;NYC_hostB:11222;NYC_hostC:11222;NYC_hostD:11222")

| Use the following methods to switch Hot Rod clients to the default cluster or to a cluster at a different site: `RemoteCacheManager.switchToDefaultCluster()` `RemoteCacheManager.switchToCluster(${site.name})`

Reference

- org.infinispan.client.hotrod.configuration package description

- org.infinispan.client.hotrod.configuration.ConfigurationBuilder

- org.infinispan.client.hotrod.RemoteCacheManager

## 3. Performing Cross-Site Replication Operations

Bring sites online and offline. Transfer cache state to remote sites.

### 3.1. Performing Cross-Site Operations with the CLI

The Infinispan command line interface lets you remotely connect to Infinispan servers, manage sites, and push state transfer to backup locations.

Prerequisites

- Start the Infinispan CLI.

- Connect to a running Infinispan cluster.

#### 3.1.1. Bringing Backup Locations Offline and Online

Take backup locations offline manually and bring them back online.

Procedure

1. Create a CLI connection to Infinispan.

2. Check if backup locations are online or offline with the `site status` command:

       [//containers/default]> site status --cache=cacheName --site=NYC

   | `--site` is an optional argument. If not set, the CLI returns all backup locations.

3. Manage backup locations as follows:

   - Bring backup locations online with the `bring-online` command:

         [//containers/default]> site bring-online --cache=customers --site=NYC

   - Take backup locations offline with the `take-offline` command:

         [//containers/default]> site take-offline --cache=customers --site=NYC

For more information and examples, run the `help site` command.

#### 3.1.2. Configuring Cross-Site State Transfer Modes

You can configure cross-site state transfer operations to happen automatically when Infinispan detects that backup locations come online. Alternatively you can use the default mode, which is to manually perform state transfer through the CLI or via JMX or REST.

Procedure

1. Create a CLI connection to Infinispan.

2. Use the `site` command to configure state transfer modes, as in the following examples:

   - Retrieve the current state transfer mode.

         [//containers/default]> site state-transfer-mode get --cache=cacheName --site=NYC
         "MANUAL"

   - Configure automatic state transfer operations for a cache and backup location.

    [//containers/default]> site state-transfer-mode set --cache=cacheName --site=NYC --mode=AUTO

| Run the `help site` command for more information and examples.

#### 3.1.3. Pushing State to Backup Locations

Transfer cache state to remote backup locations.

Procedure

1. Create a CLI connection to Infinispan.

2. Use the `site` command to push state transfer, as in the following example:

       [//containers/default]> site push-site-state --cache=cacheName --site=NYC

For more information and examples, run the `help site` command.

Reference

Infinispan Command Line Interface

### 3.2. Performing Cross-Site Operations with the REST API

Infinispan servers provide a REST API that allows you to perform cross-site operations.

#### 3.2.1. Getting Status of All Backup Locations

Retrieve the status of all backup locations with `GET` requests.

    GET /v2/caches/{cacheName}/x-site/backups/

Infinispan responds with the status of each backup location in JSON format, as in the following example:

    {
      "NYC": "online",
      "LON": "offline"
    }

Table 1. Returned Status
Value | Description
--- | ---
`online` | All nodes in the local cluster have a cross-site view with the backup location.
`offline` | No nodes in the local cluster have a cross-site view with the backup location.
`mixed` | Some nodes in the local cluster have a cross-site view with the backup location, other nodes in the local cluster do not have a cross-site view. The response indicates status for each node.

#### 3.2.2. Getting Status of Specific Backup Locations

Retrieve the status of a backup location with `GET` requests.

    GET /v2/caches/{cacheName}/x-site/backups/{siteName}

Infinispan responds with the status of each node in the site in JSON format, as in the following example:

    {
      "NodeA":"offline",
      "NodeB":"online"
    }

Table 2. Returned Status
Value | Description
--- | ---
`online` | The node is online.
`offline` | The node is offline.
`failed` | Not possible to retrieve status. The remote cache could be shutting down or a network error occurred during the request.

#### 3.2.3. Taking Backup Locations Offline

Take backup locations offline with `POST` requests and the `?action=take-offline` parameter.

    POST /v2/caches/{cacheName}/x-site/backups/{siteName}?action=take-offline

#### 3.2.4. Bringing Backup Locations Online

Bring backup locations online with the `?action=bring-online` parameter.

    POST /v2/caches/{cacheName}/x-site/backups/{siteName}?action=bring-online

#### 3.2.5. Pushing State to Backup Locations

Push cache state to a backup location with the `?action=start-push-state` parameter.

    POST /v2/caches/{cacheName}/x-site/backups/{siteName}?action=start-push-state

#### 3.2.6. Canceling State Transfer

Cancel state transfer operations with the `?action=cancel-push-state` parameter.

    POST /v2/caches/{cacheName}/x-site/backups/{siteName}?action=cancel-push-state

#### 3.2.7. Getting State Transfer Status

Retrieve status of state transfer operations with the `?action=push-state-status` parameter.

    GET /v2/caches/{cacheName}/x-site/backups?action=push-state-status

Infinispan responds with the status of state transfer for each backup location in JSON format, as in the following example:

    {
       "NYC":"CANCELED",
       "LON":"OK"
    }

Table 3. Returned Status
Value | Description
--- | ---
`SENDING` | State transfer to the backup location is in progress.
`OK` | State transfer completed successfully.
`ERROR` | An error occurred with state transfer. Check log files.
`CANCELLING` | State transfer cancellation is in progress.

#### 3.2.8. Clearing State Transfer Status

Clear state transfer status for sending sites with the `?action=clear-push-state-status` parameter.

    POST /v2/caches/{cacheName}/x-site/local?action=clear-push-state-status

#### 3.2.9. Modifying Take Offline Conditions

Sites go offline if certain conditions are met. Modify the take offline parameters to control when backup locations automatically go offline.

Procedure

1. Check configured take offline parameters with `GET` requests and the `take-offline-config` parameter.

       GET /v2/caches/{cacheName}/x-site/backups/{siteName}/take-offline-config

   The Infinispan response includes `after_failures` and `min_wait` fields as follows:

       {
         "after_failures": 2,
         "min_wait": 1000
       }

2. Modify take offline parameters in the body of `PUT` requests.

       PUT /v2/caches/{cacheName}/x-site/backups/{siteName}/take-offline-config

   If the operation successfully completes, the service returns `204 (No Content)`.

#### 3.2.10. Canceling State Transfer from Receiving Sites

If the connection between two backup locations breaks, you can cancel state transfer on the site that is receiving the push.

Cancel state transfer from a remote site and keep the current state of the local cache with the `?action=cancel-receive-state` parameter.

    POST /v2/caches/{cacheName}/x-site/backups/{siteName}?action=cancel-receive-state

#### 3.2.11. Getting Status of Backup Locations

Retrieve the status of all backup locations from Cache Managers with `GET` requests.

    GET /rest/v2/cache-managers/{cacheManagerName}/x-site/backups/

Infinispan responds with status in JSON format, as in the following example:

    {
       "SFO-3":{
          "status":"online"
       },
       "NYC-2":{
          "status":"mixed",
          "online":[
             "CACHE_1"
          ],
          "offline":[
             "CACHE_2"
          ]
       }
    }

Table 4. Returned Status
Value | Description
--- | ---
`online` | All nodes in the local cluster have a cross-site view with the backup location.
`offline` | No nodes in the local cluster have a cross-site view with the backup location.
`mixed` | Some nodes in the local cluster have a cross-site view with the backup location, other nodes in the local cluster do not have a cross-site view. The response indicates status for each node.

#### 3.2.12. Taking Backup Locations Offline

Take backup locations offline with the `?action=take-offline` parameter.

    POST /rest/v2/cache-managers/{cacheManagerName}/x-site/backups/{siteName}?action=take-offline

#### 3.2.13. Bringing Backup Locations Online

Bring backup locations online with the `?action=bring-online` parameter.

    POST /rest/v2/cache-managers/{cacheManagerName}/x-site/backups/{siteName}?action=bring-online

#### 3.2.14. Retrieving the State Transfer Mode

Check the state transfer mode with `GET` requests.

    GET /rest/v2/caches/{cacheName}/x-site/backups/{site}/state-transfer-mode

#### 3.2.15. Setting the State Transfer Mode

Configure the state transfer mode with the `?action=set` parameter.

    POST /rest/v2/caches/{cacheName}/x-site/backups/{site}/state-transfer-mode?action=set&mode={mode}

#### 3.2.16. Starting State Transfer

Push state of all caches to remote sites with the `?action=start-push-state` parameter.

    POST /rest/v2/cache-managers/{cacheManagerName}/x-site/backups/{siteName}?action=start-push-state

#### 3.2.17. Canceling State Transfer

Cancel ongoing state transfer operations with the `?action=cancel-push-state` parameter.

    POST /rest/v2/cache-managers/{cacheManagerName}/x-site/backups/{siteName}?action=cancel-push-state

### 3.3. Performing Cross-Site Operations with JMX

Infinispan provides JMX tooling to perform cross-site operations such as pushing state transfer and bringing sites online.

#### 3.3.1. Configuring Infinispan to Register JMX MBeans

Infinispan can register JMX MBeans that you can use to collect statistics and perform administrative operations. You must enable statistics separately to JMX otherwise Infinispan provides `0` values for all statistic attributes.

Procedure

Modify your cache container configuration to enable JMX in one of the following ways:

- Declarative: Add the `<jmx enabled="true" />` element to the cache container.

- Programmatic: Call the `.jmx().enable()` method.

Declarative

    <cache-container>
      <jmx enabled="true" />
    </cache-container>

Programmatic

    GlobalConfiguration globalConfig = new GlobalConfigurationBuilder()
      .jmx().enable()
      .build();

#### 3.3.2. Performing Cross-Site Operations

Perform cross-site operations via JMX clients.

Prerequisites

- Configure Infinispan to register JMX MBeans

Procedure

1. Connect to Infinispan with any JMX client.

2. Invoke operations from the following MBeans:

   - `XSiteAdmin` provides cross-site operations for caches.

   - `GlobalXSiteAdminOperations` provides cross-site operations for Cache Managers.

     For example, to bring sites back online, invoke `bringSiteOnline(siteName)`.

See the Infinispan JMX Components documentation for details about available cross-site operations.

Reference

- XSiteAdmin MBean

- GlobalXSiteAdminOperations MBean

## 4. Monitoring and Troubleshooting Global Infinispan Clusters

Infinispan provides statistics for cross-site replication operations via JMX or the `/metrics` endpoint for Infinispan server.

Cross-site replication statistics are available at cache level so you must explicitly enable statistics for your caches. Likewise, if you want to collect statistics via JMX you must configure Infinispan to register MBeans.

Infinispan also includes an `org.infinispan.XSITE` logging category so you can monitor and troubleshoot common issues with networking and state transfer operations.

### 4.1. Enabling Infinispan Statistics

Configure Infinispan to export statistics for Cache Managers and caches.

Procedure

Modify your configuration to enable Infinispan statistics in one of the following ways:

- Declarative: Add the `statistics="true"` attribute.

- Programmatic: Call the `.statistics()` method.

Declarative

    <!-- Enables statistics for the Cache Manager. -->
    <cache-container statistics="true">
      <!-- Enables statistics for the named cache. -->
      <local-cache name="mycache" statistics="true"/>
    </cache-container>

Programmatic

    GlobalConfiguration globalConfig = new GlobalConfigurationBuilder()
      //Enables statistics for the Cache Manager.
      .cacheContainer().statistics(true)
      .build();

    Configuration config = new ConfigurationBuilder()
      //Enables statistics for the named cache.
      .statistics().enable()
      .build();

### 4.2. Configuring Infinispan Metrics

Configure Infinispan to export gauges and histograms via the `metrics` endpoint.

Procedure

- Turn gauges and histograms on or off in the `metrics` configuration as appropriate.

Declarative

    <!-- Computes and collects statistics for the Cache Manager. -->
    <cache-container statistics="true">
      <!-- Exports collected statistics as gauge and histogram metrics. -->
      <metrics gauges="true" histograms="true" />
    </cache-container>

Programmatic

    GlobalConfiguration globalConfig = new GlobalConfigurationBuilder()
      //Computes and collects statistics for the Cache Manager.
      .statistics().enable()
      //Exports collected statistics as gauge and histogram metrics.
      .metrics().gauges(true).histograms(true)
      .build();

#### 4.2.1. Collecting Infinispan Metrics

Collect Infinispan metrics with monitoring tools such as Prometheus.

Prerequisites

- Enable statistics. If you do not enable statistics, Infinispan provides `0` and `-1` values for metrics.

- Optionally enable histograms. By default Infinispan generates gauges but not histograms.

Procedure

- Get metrics in Prometheus (OpenMetrics) format:

      $ curl -v http://localhost:11222/metrics

- Get metrics in MicroProfile JSON format:

      $ curl --header "Accept: application/json" http://localhost:11222/metrics

Next steps

Configure monitoring applications to collect Infinispan metrics. For example, add the following to `prometheus.yml`:

    static_configs:
        - targets: ['localhost:11222']

Reference

- Prometheus Configuration

- Enabling Infinispan Statistics

### 4.3. Configuring Infinispan to Register JMX MBeans

Infinispan can register JMX MBeans that you can use to collect statistics and perform administrative operations. You must enable statistics separately to JMX otherwise Infinispan provides `0` values for all statistic attributes.

Procedure

Modify your cache container configuration to enable JMX in one of the following ways:

- Declarative: Add the `<jmx enabled="true" />` element to the cache container.

- Programmatic: Call the `.jmx().enable()` method.

Declarative

    <cache-container>
      <jmx enabled="true" />
    </cache-container>

Programmatic

    GlobalConfiguration globalConfig = new GlobalConfigurationBuilder()
      .jmx().enable()
      .build();

#### 4.3.1. JMX MBeans for Cross-Site Replication

Infinispan provides JMX MBeans for cross-site replication that let you gather statistics and perform remote operations.

The `org.infinispan:type=Cache` component provides the following JMX MBeans:

- `XSiteAdmin` exposes cross-site operations that apply to specific cache instances.

- `StateTransferManager` provides statistics for state transfer operations.

- `InboundInvocationHandler` provides statistics and operations for asynchronous and synchronous cross-site requests.

The `org.infinispan:type=CacheManager` component includes the following JMX MBean:

- `GlobalXSiteAdminOperations` exposes cross-site operations that apply to all caches in a cache container.

For details about JMX MBeans along with descriptions of available operations and statistics, see the Infinispan JMX Components documentation.

Reference

Infinispan JMX Components

### 4.4. Collecting Logs and Troubleshooting Cross-Site Replication

Diagnose and resolve issues related to Infinispan cross-site replication. Use the Infinispan Command Line Interface (CLI) to adjust log levels at run-time and perform cross-site troubleshooting.

Procedure

1. Open a terminal in `$ISPN_HOME`.

2. Create a Infinispan CLI connection.

3. Adjust run-time logging levels to capture DEBUG messages if necessary.

   For example, the following command enables DEBUG log messages for the org.infinispan.XSITE category:

       [//containers/default]> logging set --level=DEBUG org.infinispan.XSITE

   You can then check the Infinispan log files for cross-site messages in the `${infinispan.server.root}/log` directory.

4. Use the `site` command to view status for backup locations and perform troubleshooting.

For example, check the status of the "customers" cache that uses "LON" as a backup location:

    [//containers/default]> site status --cache=customers
    {
      "LON" : "online"
    }

Another scenario for using the Infinispan CLI to troubleshoot is when the network connection between backup locations is broken during a state transfer operation.

If this occurs, Infinispan clusters that receive state transfer continually wait for the operation to complete. In this case you should cancel the state transfer to the receiving site to return it to a normal operational state.

For example, cancel state transfer for "NYC" as follows:

    [//containers/default]> site cancel-receive-state --cache=mycache --site=NYC`

Reference

- Infinispan Server Troubleshooting

- Working with Infinispan Server Logs

#### 4.4.1. Cross-Site Log Messages

Find user actions for log messages related to cross-site replication.

Log level | Identifier | Message | Description
--- | --- | --- | ---
DEBUG | ISPN000400 | Node null was suspected | Infinispan prints this message when it cannot reach backup locations. Ensure that sites are online and check network status.
INFO | ISPN000439 | Received new x-site view: ${site.name} | Infinispan prints this message when sites join and leave the global cluster.
INFO | ISPN100005 | Site ${site.name} is online. | Infinispan prints this message when a site comes online.
INFO | ISPN100006 | Site ${site.name} is offline. | Infinispan prints this message when a site goes offline. If you did not take the site offline manually, this message could indicate a failure has occurred. Check network status and try to bring the site back online.
WARN | ISPN000202 | Problems backing up data for cache ${cache.name} to site ${site.name}: | Infinispan prints this message when issues occur with state transfer operations along with the exception. If necessary adjust Infinispan logging to get more fine-grained logging messages.
WARN | ISPN000289 | Unable to send X-Site state chunk to ${site.name}. | Indicates that Infinispan cannot transfer a batch of cache entries during a state transfer operation. Ensure that sites are online and check network status.
WARN | ISPN000291 | Unable to apply X-Site state chunk. | Indicates that Infinispan cannot apply a batch of cache entries during a state transfer operation. Ensure that sites are online and check network status.
WARN | ISPN000322 | Unable to re-start x-site state transfer to site ${site.name} | Indicates that Infinispan cannot resume a state transfer operation to a backup location. Ensure that sites are online and check network status.
ERROR | ISPN000477 | Unable to perform operation ${operation.name} for site ${site.name} | Indicates that Infinispan cannot successfully complete an operation on a backup location. If necessary adjust Infinispan logging to get more fine-grained logging messages.
FATAL | ISPN000449 | XSite state transfer timeout must be higher or equals than 1 (one). | Results when the value of the `timeout` attribute is `0` or a negative number. Specify a value of at least `1` for the `timeout` attribute in the state transfer configuration for your cache definition.
FATAL | ISPN000450 | XSite state transfer waiting time between retries must be higher or equals than 1 (one). | Results when the value of the `wait-time` attribute is `0` or a negative number. Specify a value of at least `1` for the `wait-time` attribute in the state transfer configuration for your cache definition.
FATAL | ISPN000576 | Cross-site Replication not available for local cache. | Cross-site replication does not work with the local cache mode. Either remove the backup configuration from the local cache definition or use a distributed or replicated cache mode.