[[Undertow]]
= Undertow Subsystem

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****

*Web subsystem was replaced in WildFly 8 with Undertow.*

****

There are two main parts to the undertow subsystem, which are server and
Servlet container configuration, as well as some ancillary items.
Advanced topics like load balancing and failover are covered on the
"High Availability Guide". The default configuration does is suitable
for most use cases and provides reasonable performance settings.

*Required extension:*

[source,xml,options="nowrap"]
----
<extension module="org.wildfly.extension.undertow" />
----

*Basic subsystem configuration example:*

[source,xml,options="nowrap"]
----
<subsystem xmlns="urn:jboss:domain:undertow:13.0">
        <buffer-cache name="default" buffer-size="1024" buffers-per-region="1024" max-regions="10"/>
        <server name="default-server">
            <http-listener name="default" socket-binding="http" />
            <host name="default-host" alias="localhost">
                <location name="/" handler="welcome-content" />
            </host>
        </server>
        <servlet-container name="default" default-buffer-cache="default" stack-trace-on-error="local-only" >
            <jsp-config/>
            <persistent-sessions/>
        </servlet-container>
        <handlers>
            <file name="welcome-content" path="${jboss.home.dir}/welcome-content" directory-listing="true"/>
        </handlers>
    </subsystem>
----
[cols=",",options="header"]
|=======================================================================
|Attribute |Description
|default-server | the default server to use for deployments
|default-virtual-host | the default virtual host to use for deployments
|default-servlet-container | the default servlet container to use for deployments
|instance-id | the id of Undertow. Defaults to "${jboss.node.name}" if undefined
|[[bookmark-obfuscate-session-route]]obfuscate-session-route | set this to `"true"` to indicate the
`instance-id` should be obfuscated in routing. This prevents `instance-id` from being sent across
HTTP connections when serving remote requests with the HTTP invoker.
|default-security-domain |the default security domain used by web deployments
|statistics-enabled | set this to true to enable statistics gathering for Undertow subsystem
|=======================================================================

[NOTE]
====
When setting <<bookmark-obfuscate-session-route,`obfuscate-session-route`>> to `"true"`, the server's
<<bookmark-server-name,`name`>> is used as a salt in the hashing algorithm that obfuscates the value of `instance-id`.
For that reason, it is strongly advised that the value of the server be changed from `"default-server"` to something
else, or else it would be easy to reverse engineer the obfuscated route to its original value, using `"default-server"`
bytes as the salt.
====

*Dependencies on other subsystems:*

IO Subsystem

[[buffer-cache-configuration]]
== Buffer cache configuration

The buffer cache is used for caching content, such as static files.
Multiple buffer caches can be configured, which allows for separate
servers to use different sized caches.

Buffers are allocated in regions, and are of a fixed size. If you are
caching many small files then using a smaller buffer size will be
better.

The total amount of space used can be calculated by multiplying the
buffer size by the number of buffers per region by the maximum number of
regions.

[source,xml,options="nowrap"]
----
  <buffer-caches>
    <buffer-cache name="default" buffer-size="1024" buffers-per-region="1024" max-regions="10"/>
  </buffer-caches>
----

[cols=",",options="header"]
|=======================================================================
|Attribute |Description

|buffer-size |The size of the buffers. Smaller buffers allow space to be
utilised more effectively

|buffers-per-region |The numbers of buffers per region

|max-regions |The maximum number of regions. This controls the maximum
amount of memory that can be used for caching
|=======================================================================

[[server-configuration]]
== Server configuration

A server represents an instance of Undertow. Basically this consists of
a set of connectors and some configured handlers.

[source,xml,options="nowrap"]
----
<server name="default-server" default-host="default-host" servlet-container="default" >
----

[cols=",",options="header"]
|=======================================================================
|Attribute |Description

|[[bookmark-server-name]]name| the name of this server

|default-host |the virtual host that will be used if an incoming request
as no Host: header

|servlet-container |the servlet container that will be used by this
server, unless is is explicitly overriden by the deployment
|=======================================================================

[[connector-configuration]]
=== Connector configuration

Undertow provides HTTP, HTTPS and AJP connectors, which are configured
per server.

[[common-settings]]
==== Common settings

The following settings are common to all connectors:

[cols=",",options="header"]
|=======================================================================
|Attribute |Description

|allow-encoded-slash
|If a request comes in with encoded / characters (i.e. %2F), will these be decoded.

|allow-equals-in-cookie-value
|If this is true then Undertow will allow non-escaped equals characters in unquoted cookie values.
Unquoted cookie values may not contain equals characters. If present the value ends before the
equals sign. The remainder of the cookie value will be dropped.

|allow-unescaped-characters-in-url
|If this is true Undertow will accept non-encoded characters that are disallowed by the URI specification.
This defaults to false, and in general should not be needed as most clients correctly encode characters.
Note that setting this to true can be considered a security risk, as allowing non-standard characters can 
allow request smuggling attacks in some circumstances.

|always-set-keep-alive
|If this is true then a Connection: keep-alive header will be added to responses, even when it is not
strictly required by the specification.

|buffer-pipelined-data
|If we should buffer pipelined requests.

|buffer-pool
|The listeners buffer pool

|certificate-forwarding
|If certificate forwarding should be enabled. If this is enabled then the listener will take the certificate
from the SSL_CLIENT_CERT attribute. This should only be enabled if behind a proxy, and the proxy is
configured to always set these headers.

|decode-url
|If this is true then the parser will decode the URL and query parameters using the selected character
encoding (UTF-8 by default). If this is false they will not be decoded. This will allow a later handler to
decode them into whatever charset is desired.

|disallowed-methods
|A comma separated list of HTTP methods that are not allowed

|enable-http2
|Enables HTTP2 support for this listener

|enabled (Deprecated)
|If the listener is enabled

|http2-enable-push
|If server push is enabled for this connection

|http2-header-table-size
|The size of the header table used for HPACK compression, in bytes. This amount of memory will be allocated
per connection for compression. Larger values use more memory but may give better compression.

|http2-initial-window-size
|The flow control window size that controls how quickly the client can send data to the server

|http2-max-concurrent-streams
|The maximum number of HTTP/2 streams that can be active at any time on a single connection

|http2-max-frame-size
|The max HTTP/2 frame size

|http2-max-header-list-size
|The maximum size of request headers the server is prepared to accept

|max-buffered-request-size
|Maximum size of a buffered request, in bytes. Requests are not usually buffered, the most common case is 
when performing SSL renegotiation for a POST request, and the post data must be fully buffered in order 
to perform the renegotiation.

|max-connections
|The maximum number of concurrent connections. Only values greater than 0 are allowed. For unlimited
connections simply undefine this attribute value.

|max-cookies
|The maximum number of cookies that will be parsed. This is used to protect against hash vulnerabilities.

|max-header-size
|The maximum size of a http request header, in bytes.

|max-headers
|The maximum number of headers that will be parsed. This is used to protect against hash vulnerabilities.

|max-parameters
|The maximum number of parameters that will be parsed. This is used to protect against hash vulnerabilities.
This applies to both query parameters, and to POST data, but is not cumulative (i.e. you can potentially
have max parameters * 2 total parameters).

|max-post-size
|The maximum size of a post that will be accepted, in bytes.

|no-request-timeout
|The length of time in milliseconds that the connection can be idle before it is closed by the container.

|proxy-address-forwarding
|Enables  handling of x-forwarded-host header (and other x-forwarded-* headers) and use this header information
to set the remote address. This should only be used behind a trusted proxy that sets these headers otherwise
a remote user can spoof their IP address.

|proxy-protocol
|If this is true then the listener will use the proxy protocol v1, as defined by 
https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt. This option MUST only be enabled for listeners 
that are behind a load balancer that supports the same protocol.

|read-timeout
|Configure a read timeout for a socket, in milliseconds.  If the given amount of time elapses without a 
successful read taking place, the socket's next read will throw a {@link ReadTimeoutException}.

|receive-buffer
|The receive buffer size, in bytes.

|record-request-start-time
|If this is true then Undertow will record the request start time, to allow for request time to be logged.
This has a small but measurable performance impact

|request-parse-timeout
|The maximum amount of time (in milliseconds) that can be spent parsing the request

|require-host-http11
|Require that all HTTP/1.1 requests have a 'Host' header, as per the RFC. IF the request does not include
this header it will be rejected with a 403.

|resolve-peer-address
|Enables host dns lookup

|rfc6265-cookie-validation
|If cookies should be validated to ensure they comply with RFC6265.

|secure
|If this is true then requests that originate from this listener are marked as secure, even if the request
is not using HTTPS.

|send-buffer
|The send buffer size, in bytes.

|socket-binding
|The listener socket binding

|tcp-backlog
|Configure a server with the specified backlog.

|tcp-keep-alive
|Configure a channel to send TCP keep-alive messages in an implementation-dependent manner.

|url-charset
|URL charset

|worker
|The listeners XNIO worker

|write-timeout
|Configure a write timeout for a socket, in milliseconds.  If the given amount of time 
elapses without a successful write taking place, the socket's next write will throw
a {@link WriteTimeoutException}.

|=======================================================================

[[http-connector]]
==== HTTP Connector

[source,xml,options="nowrap"]
----
<http-listener name="default" socket-binding="http"  />
----

[cols=",",options="header"]
|=======================================================================
|Attribute |Description

|redirect-socket
|If this listener is supporting non-SSL requests, and a request is received for which a matching 
<security-constraint> requires SSL transport, undertow will automatically redirect the request to the 
socket binding port specified here.

|=======================================================================

[[https-listener]]
==== HTTPS listener

Https listener provides secure access to the server. The most important
configuration option is ssl-context which cross references a pre-configured
SSL Context instance.

[source,xml,options="nowrap"]
----
<https-listener name="https" socket-binding="https" ssl-context="applicationSSC" enable-http2="true"/>
----

[cols=",",options="header"]
|=======================================================================
|Attribute |Description

|enable-spdy (Deprecated) 
|Enables SPDY support for this listener. This has been deprecated and has no effect, HTTP/2 should be used instead

|enabled-cipher-suites (Deprecated)
|Where an SSLContext is referenced it should be configured with the cipher suites to be supported.

|enabled-protocols (Deprecated)
|Configures SSL protocols

|security-realm (Deprecated)
|The listeners security realm

|ssl-context
|Reference to the SSLContext to be used by this listener.

|ssl-session-cache-size (Deprecated)
|The maximum number of active SSL sessions

|ssl-session-timeout (Deprecated)
|The timeout for SSL sessions, in seconds

|verify-client (Deprecated)
|The desired SSL client authentication mode for SSL channels



|=======================================================================

[[ajp-listener]]
==== AJP listener

[source,xml,options="nowrap"]
----
<ajp-listener name="default" socket-binding="ajp" />
----

[[host-configuration]]
=== Host configuration

The host element corresponds to a virtual host.

[cols=",",options="header"]
|=======================================================================
|Attribute |Description

|name |The virtual host name

|alias |A whitespace separated list of additional host names that should
be matched

|default-web-module |The name of a deployment that should be used to
serve up requests that do not match anything.

|queue-requests-on-start| If requests should be queued on start for this host. If this is set to false the default
response code will be returned instead.

Note: If a <<non-graceful-startup>> is requested, and the queue-requests-on-start attribute is not set, requests will NOT be
queued despite the default value of true for the property. In the instance of a non-graceful startup, non-queued requests
are required. However, if non-graceful is configured, but queue-requests-on-start is explicitly set to true, then requests
will be queued, effectively disabling the non-graceful mode for requests to that host.

|=======================================================================

==== Console Access Logging

Each host allows for access logging to the console which writes structured data in JSON format. This only writes to
`stdout` and is a single line of JSON structured data.

The `attributes` management model attribute is used to determine which exchange attributes should be logged. This is
similar to the `pattern` used for traditional access logging. The main difference being since the data is structured
the ability to use defined keys is essential.

A `metadata` attribute also exists which allows extra metadata to be added to the output. The value of the attribute is
a set of arbitrary key/value pairs. The values can include management model expressions, which must be resolvable when
the console access log service is started. The value is resolved once per start or reload of the server.


===== CLI Examples

.add-console-access-logging.cli
----
/subsystem=undertow/server=default-server/host=default-host/setting=console-access-log:add
----

.complex-add-console-access-logging.cli
----
/subsystem=undertow/server=default-server/host=default-host/setting=console-access-log:add(metadata={"@version"="1", "qualifiedHostName"=${jboss.qualified.host.name:unknown}}, attributes={bytes-sent={}, date-time={key="@timestamp", date-format="yyyy-MM-dd'T'HH:mm:ssSSS"}, remote-host={}, request-line={}, response-header={key-prefix="responseHeader", names=["Content-Type"]}, response-code={}, remote-user={}})
----

[source,json]
----
{
    "eventSource":"web-access",
    "hostName":"default-host",
    "@version":"1",
    "qualifiedHostName":"localhost.localdomain",
    "bytesSent":1504,
    "@timestamp":"2019-05-02T11:57:37123",
    "remoteHost":"127.0.0.1",
    "remoteUser":null,
    "requestLine":"GET / HTTP/2.0",
    "responseCode":200,
    "responseHeaderContent-Type":"text/html"
}
----

NOTE: The above JSON is formatted only for readability. The output will be on a single line.


[[servlet-container-configuration]]
== Servlet container configuration

The servlet-container element corresponds to an instance of an Undertow
Servlet container. Most servers will only need a single servlet
container, however there may be cases where it makes sense to define
multiple containers (in particular if you want applications to be
isolated, so they cannot dispatch to each other using the
RequestDispatcher. You can also use multiple Servlet containers to serve
different applications from the same context path on different virtual
hosts).

[cols=",",options="header"]
|=======================================================================
|Attribute |Description

|allow-non-standard-wrappers |The Servlet specification requires
applications to only wrap the request/response using wrapper classes
that extend from the ServletRequestWrapper and ServletResponseWrapper
classes. If this is set to true then this restriction is relaxed.

|default-buffer-cache |The buffer cache that is used to cache static
resources in the default Servlet.

|stack-trace-on-error |Can be either all, none, or local-only. When set
to none Undertow will never display stack traces. When set to All
Undertow will always display them (not recommended for production use).
When set to local-only Undertow will only display them for requests from
local addresses, where there are no headers to indicate that the request
has been proxied. Note that this feature means that the Undertow error
page will be displayed instead of the default error page specified in
web.xml.

|default-encoding |The default encoding to use for requests and
responses.

|use-listener-encoding |If this is true then the default encoding will
be the same as that used by the listener that received the request.

| preserve-path-on-forward | If this is `true`, the return values of the
`getServletPath()`, `getRequestURL()` and `getRequestURI()` methods from
 `HttpServletRequest` will be unchanged following a
 `RequestDispatcher.forward()` call, and point to the original resource requested.
If `false`, following the `RequestDispatcher.forward()` call, they will
point to the resource being forwarded to.


|=======================================================================

[[Jakarta-Server-Pages-configuration]]
=== Jakarta Server Pages configuration

[[session-cookie-configuration]]
=== Session Cookie Configuration

This allows you to change the attributes of the session cookie.

[cols=",",options="header"]
|======================================
|Attribute |Description
|name |The cookie name
|domain |The cookie domain
|http-only |If the cookie is HTTP only
|secure |If the cookie is marked secure
|max-age |The max age of the cookie
|======================================

[[affinity-cookie-configuration]]
=== Affinity Cookie Configuration

This allows you to change the attributes of the affinity cookie.
If the affinity cookie is configured, the affinity will not be appended to the session ID, but will be sent via the configured cookie name.

[cols=",",options="header"]
|======================================
|Attribute |Description
|name (required) |The affinity cookie name
|domain |The affinity cookie domain
|http-only |If the affinity cookie is HTTP only
|secure |If the affinity cookie is marked secure
|max-age |The max age of the affinity cookie
|======================================

[[persistent-session-configuration]]
=== Persistent Session Configuration

Persistent sessions allow session data to be saved across redeploys and
restarts. This feature is enabled by adding the persistent-sessions
element to the server config. This is mostly intended to be a
development time feature.

If the path is not specified then session data is stored in memory, and
will only be persistent across redeploys, rather than restarts.

[cols=",",options="header"]
|======================================================
|Attribute |Description
|path |The path to the persistent sessions data
|relative-to |The location that the path is relevant to
|======================================================

:leveloffset: +1

include::Undertow_AJP_listeners.adoc[]

include::Undertow_using_as_a_Load_Balancer.adoc[]

:leveloffset: -1
