Server configuration overview

The Open Liberty server configuration is made up of one mandatory file, the server.xml file, and a set of optional files. The server.xml file must be well-formed XML and the root element must be server. When the server.xml file is processed, any elements or attributes that are not understood are ignored.

This example server.xml file configures the server to do the following things:

<server description="new server">
    <featureManager>
        <feature>jsp-2.3</feature>
    </featureManager>
    <httpEndpoint id="defaultHttpEndpoint"
                  httpPort="9080"
                  httpsPort="9443" />
    <applicationManager autoExpand="true" />
</server>

  • The feature element configures Open Liberty to support the JavaServer Pages 2.3 (jsp-2.3) feature.

  • The httpPort attribute is set to 9080, which configures Open Liberty to listen to incoming traffic to localhost on port 9080.

  • The autoExpand attribute is set to true so that WAR files are automatically expanded when they are deployed.

The term server configuration can be used to refer to all of the files that make up the server configuration or specifically to the configuration that’s in the XML files. If it’s not clear in context, the term server XML configuration might be used to refer to the configuration in the XML files.

The following sections provide more details on configuring a server.

Configuration files

The server configuration files are processed in the following order:

  1. server.env - Environment variables are specified in this file.

  2. jvm.options - JVM options are set in this file.

  3. bootstrap.properties - This file influences the startup of the Open Liberty server.

  4. server.xml - This mandatory file specifies the server configuration and features.

server.env

The server.env files are optional. These files are read by the bin/server shell script and specify the environment variables that are primarily used to influence the behavior of the bin/server script. The server.env files are read from the following locations in order:

  1. ${wlp.install.dir}/etc/

  2. ${wlp.user.dir}/shared/

  3. ${server.config.dir}/

If the same property is set in multiple locations, then the last value that is found is used. You can also specify these environment variables in the shell environment, but the server.env files take precedence over those variables.

The most common use of these files is to set the following environment variables:

  • JAVA_HOME - Indicates which JVM to use. If the JVM is not set, the system default is used.

  • WLP_USER_DIR - Indicates the location of the usr directory that contains the server configuration. Set this environment variable only in the etc/server.env file, because other locations are relative to the usr directory.

  • WLP_OUTPUT_DIR - Indicates where the server writes files. By default, the server writes to the directory structure from which the configuration is read. However, in some secure profiles, the server configuration is read-only so the server must write files to another location.

The server.env file is in KEY=value format, as shown in the following example:

JAVA_HOME=/opt/ibm/java
WLP_USER_DIR=/opt/wlp-usr

The following restrictions apply to the server.env files:

  • Key values must not contain any spaces.

  • Empty lines are ignored.

  • Lines that start with the number sign ( # ) are ignored, except for the # enable_variable_expansion line, which enables variable expansion on Linux.

  • Ensure no white space surrounds the equal sign ( = ).

  • All characters are literal except when expansion variables are enabled.

For more information, see Default environment variables.

Expansion variables

Expansion variables are environment or shell variables that are replaced by their values. You can specify expansion variables in the value definition of other variables. The values that these expansion variables supply can be defined as environment variables in your server configuration or shell variables in your shell environment. The caret sign ( ^ ) is used to escape a variable expansion character like the exclamation point (!) on Windows. The syntax for specifying expansion variables is operating system dependent.

Variable expansion support is enabled by default on Windows. You specify expansion variables by using the Windows delayed expansion syntax: !variable_name!, which is replaced by the value of the variable.

The following server.env file example shows the syntax for expansion variables on Windows.

IBM_DIR=!ProgramFiles!\IBM
JAVA_HOME=!IBM_DIR!\java
WLP_USER_DIR=!USERPROFILE!\wlp-usr

In version 22.0.0.1 and later, Open Liberty supports expansion variables in the server.env file on Linux systems. Expansion variables are prefixed by a dollar sign ( $ ) and the variable name can optionally be enclosed in curly braces ( {} ), for example, $variable_name or ${variable_name}.

When you enable expansion variables for Linux, single quotation marks ( ' ), double quotation marks ( " ), and backslash ( \ ) behave the same as in the shell environment. For example, placing a string in single quotation marks prevents the expansion of variables. Placing a string in double quotation marks does not prevent the expansion of variables, and the backslash is an escape character that removes the meaning of a special character.

By default, server.env files do not support variable expansion on Linux. The value in each KEY=value pair is interpreted literally and you do not need to escape special characters, such as spaces. However, when you enable support for variable expansion, you must escape special characters.

To enable support for variable expansion, add the following comment at the beginning of the server.env file.

# enable_variable_expansion

When expansion variables are enabled, you must enclose any values that contain spaces in quotation marks. You must also escape inner quotation marks. For example, the inner quotation mark is escaped in the following value:

MESSAGE1='Don\'t do that'

The following server.env file example shows the syntax for expansion variables on Linux. The values for the WLP_USER_DIR and LOG_DIR environment variables contain expansion variables.

# enable_variable_expansion
JAVA_HOME=/opt/ibm/java
WLP_USER_DIR=/home/${USER}/wlp-usr
LOG_DIR=${WLP_USER_DIR}/logs

jvm.options

The jvm.options files are optional. These files are read by the bin/server shell script to determine what options to use when the JVM is launched for Open Liberty. jvm.options files are read from the following locations in order:

  1. ${wlp.user.dir}/shared/jvm.options

  2. ${server.config.dir}/configDropins/defaults/

  3. ${server.config.dir}/

  4. ${server.config.dir}/configDropins/overrides/

If no jvm.options files exist in these locations, then the server script looks for the file in ${wlp.install.dir}/etc, if such a directory exists.

Common uses of jvm.options files include:

  • Setting JVM memory limits

  • Enabling Java Agents that are provided by monitoring products

  • Setting Java System Properties

The jvm.options file format uses one line per JVM option, as shown in the following example:

-Xmx512m
-Dmy.system.prop=This is the value.

You don’t need to escape special characters, such as spaces. Options are read and provided to the JVM in order. If you provide multiple options, then they are all seen by the JVM. These files do not support variable substitution.

bootstrap.properties

The bootstrap.properties file is optional.

This file is read during Open Liberty bootstrap to provide configuration for the earliest stages of the server startup. It is read by the server earlier than the server.xml file so it can affect the startup and behavior of the Open Liberty kernel from the start. The bootstrap.properties file is a simple Java properties file and is located in ${server.config.dir}. A common use of the bootstrap.properties file is to configure logging because it can affect logging behavior before the server.xml file is read.

The bootstrap.properties file supports a special optional property, bootstrap.include, which specifies another properties file to also be read during the bootstrap stage. For example, this boostrap.include file can contain a common set of bootstrap properties for multiple servers to use. Set the bootstrap.include file to an absolute or relative file path.

server.xml

The most important and only required configuration file is the server.xml file. The server.xml file must be well-formed XML and the root element must be server. The exact elements that are supported by a server depend on which features are configured, and any unknown configuration is ignored.

Open Liberty uses a principle of configuration by exception, which allows for succinct configuration files. The runtime environment operates from a set of built-in configuration default settings. You only specify configuration that overrides those default settings.

Server configuration files are read from the following locations in order:

  • ${server.config.dir}/configDropins/defaults/

  • ${server.config.dir}/server.xml

  • ${server.config.dir}/configDropins/overrides/

The ${server.config.dir}/server.xml file must be present, but the other files are optional.

You can flexibly compose configuration by dropping server-formatted XML files into directories. Files are read in alphabetical order in each of the two configDropins directories.

Configuration variable syntax

Variables define reusable values that are substituted with actual values at runtime. In Open Liberty server configuration files, you can reference variables by using the ${variable.name} syntax. The dollar sign ($) indicates the start of a variable reference. Curly brackets ({}) enclose the name of the variable.

For example, if you define a variable that is named database.url with the value jdbc:mysql://localhost:3306/mydb, you can reference it in your server configuration files by using ${database.url}. At runtime, Open Liberty replaces ${database.url} with the actual value jdbc:mysql://localhost:3306/mydb.

For more information about specifying variables, see Variable substitution precedence.

Variable substitution precedence

You can use variables to parameterize the server configuration. To resolve variable references to their values, the following sources are consulted in order, in increasing order of precedence, meaning that later sources supersede and take precedence over earlier sources:

  1. variable default values in the server.xml file

  2. environment variables

  3. bootstrap.properties

  4. Java system properties

  5. Variables loaded from files in the ${server.config.dir}/variables directory or other directories as specified by the VARIABLE_SOURCE_DIRS environment variable

  6. variable values declared in the server.xml file

  7. variables declared on the command line

Variables are referenced by using the ${variableName} syntax. Specify variables in the server configuration as shown in the following example:

<variable name="variableName" value="some.value" />

Default values, which are specified in the server.xml file, are used only if no other value is specified:

<variable name="variableName" defaultValue="some.default.value" />

You can also specify variables at startup from the command line. If you do, the variables that are specified on the command line override all other sources of variables and can’t be changed after the server starts:

server run myserver -- --variableName=variableValue

Environment variables can be accessed as variables. You can reference the environment variable name directly. If the variable cannot be resolved as specified, the server.xml file looks for the following variations on the environment variable name:

  • Replace all non-alphanumeric characters with the underscore character (_)

  • Change all characters to uppercase

For example, if you enter ${my.env.var} in the server.xml file, it looks for environment variables with the following names:

  1. my.env.var

  2. my_env_var

  3. MY_ENV_VAR

The VARIABLE_SOURCE_DIRS environment variable specifies directories from which variables can be loaded. If this environment variable is not specified, the default location for the variable directory is ${server.config.dir}/variables. To define a list of directories as the value for this variable, separate each directory with the path separator for your operating system. For Windows, the path separator is a semicolon (;). For Unix-based systems, the path separator is a colon (:).

The name of the file is used as the variable name, and the contents of the file are used as the variable value. For example, you can create a file in the variables directory that is named httpPort with the text string 9080 as the only content. You can then use the variable ${httpPort} in the server.xml file and it resolves to 9080.

If you create a file in a directory within the variables directory, then the parent directory is added to the variable name. For example, you can create a ${httpPort} file in the ports subdirectory within the variable directory, the variable name is ${ports/httpPort}.

Variables in the VARIABLE_SOURCE_DIRS directories can also be defined in properties files. If the name of the file ends in .properties, each property in the file is used to create a variable. For example, you can create a file that is named ports.properties with the following contents:

httpPort=9080
httpsPort=9443

With this configuration, you can specify the ${httpPort} and ${httpsPort} variables in your server.xml file and their values resolve to 9080 and 9443.

Variable values are always interpreted as a string with simple type conversion. Therefore, a list of ports (such as 80,443) might be interpreted as a single string rather than as two port numbers. You can force the variable substitution to split on the , by using a list function, as shown in the following example:

<mongo ports="${list(mongoPorts)}" hosts="${list(mongoHosts)}" />

Simple arithmetic is supported for variables with integer values. The left and right sides of the operator can be either a variable or a number. The operator can be +, -, *, or /, as shown in the following example:

<variable name="one" value="1" />
<variable name="two" value="${one+1}" />
<variable name="three" value="${one+two}" />
<variable name="six" value="${two*three}" />
<variable name="five" value="${six-one}" />
<variable name="threeagain" value="${six/two}" />

The following predefined variables exist:

  • wlp.install.dir - the directory where the Open Liberty runtime is installed.

  • wlp.server.name - the name of the server.

  • wlp.user.dir - the directory of the usr folder. The default is ${wlp.install.dir}/usr.

  • shared.app.dir - the directory of shared applications. The default is ${wlp.user.dir}/shared/apps.

  • shared.config.dir - the directory of shared configuration files. The default is ${wlp.user.dir}/shared/config.

  • shared.resource.dir - the directory of shared resource files. The default is ${wlp.user.dir}/shared/resources.

  • server.config.dir - the directory where the server configuration is stored. The default is ${wlp.user.dir}/servers/${wlp.server.name}.

  • server.output.dir - the directory where the server writes the workarea, logs, and other runtime-generated files. The default is ${server.config.dir}.

Configuration merging

Since the configuration can consist of multiple files, it is possible that two files provide the same configuration. In these situations, the server configuration is merged according to a set of simple rules. In Open Liberty, configuration is separated into singleton and factory configuration each of which has its own rules for merging. Singleton configuration is used to configure a single element (for example, logging). Factory configuration is used to configure multiple entities, such as an entire application or data source.

Merging singleton configuration

For singleton configuration elements that are specified more than once, the configuration is merged. If two elements exist with different attributes, both attributes are used. For example:

<server>
    <logging a="true" />
    <logging b="false" />
</server>

is treated as:

<server>
    <logging a="true" b="false" />
</server>

If the same attribute is specified twice, then the last instance takes precedence. For example:

<server>
    <logging a="true" b="true" />
    <logging b="false" />
</server>

is treated as:

<server>
    <logging a="true" b="false" />
</server>

Configuration is sometimes provided by using child elements that take text.

In these cases, the configuration is merged by using all of the values specified. The most common scenario is configuring features. For example:

<server>
    <featureManager>
        <feature>servlet-4.0</feature>
    </featureManager>
    <featureManager>
        <feature>restConnector-2.0</feature>
    </featureManager>
</server>

is treated as:

<server>
    <featureManager>
        <feature>servlet-4.0</feature>
        <feature>restConnector-2.0</feature>
    </featureManager>
</server>

Merging factory configuration

Factory configuration merges use the same rules as singleton configuration except elements are not automatically merged just because the element names match. With factory configuration it is valid to configure the same element and mean two different logical objects. Therefore, each element is assumed to configure a distinct object. If a single logical object is configured by two elements, the id attribute must be set on each element to indicate they are the same thing. Variable substitution on an id attribute is not supported.

The following example configures two applications. The first application is myapp.war, which has a context root of myawesomeapp. The other application is myapp2.war, which has myapp2 as the context root:

<server>
    <webApplication id="app1" location="myapp.war" />
    <webApplication location="myapp2.war" />
    <webApplication id="app1" contextRoot="/myawesomeapp" />
</server>

Include processing

In addition to the default locations, additional configuration files can be brought in by using the include element. When a server configuration file contains an include reference to another file, the server processes the contents of the referenced file as if they were included inline in place of the include element.

In the following example, the server processes the contents of the other.xml file before it processes the contents of the other2.xml file:

<server>
    <include location="other.xml" />
    <include location="other2.xml" />
</server>

By default, the include file must exist. If the include file might not be present, set the optional attribute to true, as shown in the following example:

<server>
    <include location="other.xml" optional="true" />
</server>

When you include a file, you can specify the onConflict attribute to change the normal merge rules. You can set the value of the onConflict attribute to IGNORE or REPLACE any conflicting config:

<server>
    <include location="other.xml" onConflict="IGNORE" />
    <include location="other2.xml" onConflict="REPLACE" />
</server>

You can set the location attribute to a relative or absolute file path, or to an HTTP URL.

Configuration references

Most configuration in Open Liberty is self-contained, but it is often useful to share configuration. For example, the JDBC driver configuration might be shared by multiple data sources. You can refer to any factory configuration element that is defined as a direct child of the server element.

A reference to configuration always uses the id attribute of the element that is being referenced. The configuration element that makes the reference uses an attribute that always ends with Ref, as shown in the following example:

<server>
  <dataSource jndiName="jdbc/fred" jdbcDriverRef="myDriver" />
  <jdbcDriver id="myDriver" />
</server>

Dynamic updates

The server monitors the server XML configuration for updates and dynamically reloads when changes are detected. Changes to non-XML files (server.env, bootstrap.properties, and jvm.options) are not dynamic because they are only read at startup. Any server XML configuration file on the local disk is monitored for updates every 500ms. You can configure the frequency of XML configuration file monitoring. For example, to configure the server to monitor every 10 minutes, specify:

<config monitorInterval="10m" />

To disable file system polling and reload only when an MBean is notified, specify:

<config updateTrigger="mbean" />

Log messages

When the server runs, it might output log messages that reference configuration. The references in the log use an XPath-like structure to specify configuration elements. The element name is given with the value of the id attribute inside square brackets. If no id is specified in the server configuration an id is automatically generated. Based on the following server XML configuration example, the dataStore element and the child dataSource are identified in the logs as dataStore[myDS] and dataStore[myDS]/dataSource[default-0].

<server>
    <dataStore id="myDS">
        <dataSource />
    </dataStore>
</server>