62. Installing Spring Boot Applications

62. Installing Spring Boot Applications
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In addition to running Spring Boot applications by using java -jar, it is also possible to make fully executable applications for Unix systems. A fully executable jar can be executed like any other executable binary or it can be registered with init.d or systemd. This makes it very easy to install and manage Spring Boot applications in common production environments.

Caution

	Caution
Fully executable jars work by embedding an extra script at the front of the file. Currently, some tools do not accept this format, so you may not always be able to use this technique. For example, `jar -xf` may silently fail to extract a jar or war that has been made fully executable. It is recommended that you make your jar or war fully executable only if you intend to execute it directly, rather than running it with `java -jar` or deploying it to a servlet container.

Fully executable jars work by embedding an extra script at the front of the file. Currently, some tools do not accept this format, so you may not always be able to use this technique. For example, jar -xf may silently fail to extract a jar or war that has been made fully executable. It is recommended that you make your jar or war fully executable only if you intend to execute it directly, rather than running it with java -jar or deploying it to a servlet container.

To create a ‘fully executable’ jar with Maven, use the following plugin configuration:

<plugin>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-maven-plugin</artifactId>
	<configuration>
		<executable>true</executable>
	</configuration>
</plugin>

The following example shows the equivalent Gradle configuration:

bootJar {
	launchScript()
}

You can then run your application by typing ./my-application.jar (where my-application is the name of your artifact). The directory containing the jar is used as your application’s working directory.

62.1 Supported Operating Systems

The default script supports most Linux distributions and is tested on CentOS and Ubuntu. Other platforms, such as OS X and FreeBSD, require the use of a custom embeddedLaunchScript.

62.2 Unix/Linux Services

Spring Boot application can be easily started as Unix/Linux services by using either init.d or systemd.

62.2.1 Installation as an `init.d` Service (System V)

If you configured Spring Boot’s Maven or Gradle plugin to generate a fully executable jar, and you do not use a custom embeddedLaunchScript, your application can be used as an init.d service. To do so, symlink the jar to init.d to support the standard start, stop, restart, and status commands.

The script supports the following features:

Starts the services as the user that owns the jar file
Tracks the application’s PID by using /var/run/<appname>/<appname>.pid
Writes console logs to /var/log/<appname>.log

Assuming that you have a Spring Boot application installed in /var/myapp, to install a Spring Boot application as an init.d service, create a symlink, as follows:

$ sudo ln -s /var/myapp/myapp.jar /etc/init.d/myapp

Once installed, you can start and stop the service in the usual way. For example, on a Debian-based system, you could start it with the following command:

$ service myapp start

	Tip
	If your application fails to start, check the log file written to `/var/log/<appname>.log` for errors.

You can also flag the application to start automatically by using your standard operating system tools. For example, on Debian, you could use the following command:

$ update-rc.d myapp defaults <priority>

Securing an `init.d` Service

	Note
	The following is a set of guidelines on how to secure a Spring Boot application that runs as an init.d service. It is not intended to be an exhaustive list of everything that should be done to harden an application and the environment in which it runs.

When executed as root, as is the case when root is being used to start an init.d service, the default executable script runs the application as the user who owns the jar file. You should never run a Spring Boot application as root, so your application’s jar file should never be owned by root. Instead, create a specific user to run your application and use chown to make it the owner of the jar file, as shown in the following example:

$ chown bootapp:bootapp your-app.jar

In this case, the default executable script runs the application as the bootapp user.

	Tip
	To reduce the chances of the application’s user account being compromised, you should consider preventing it from using a login shell. For example, you can set the account’s shell to `/usr/sbin/nologin`.

You should also take steps to prevent the modification of your application’s jar file. Firstly, configure its permissions so that it cannot be written and can only be read or executed by its owner, as shown in the following example:

$ chmod 500 your-app.jar

Second, you should also take steps to limit the damage if your application or the account that’s running it is compromised. If an attacker does gain access, they could make the jar file writable and change its contents. One way to protect against this is to make it immutable by using chattr, as shown in the following example:

$ sudo chattr +i your-app.jar

This will prevent any user, including root, from modifying the jar.

If root is used to control the application’s service and you use a .conf file to customize its startup, the .conf file is read and evaluated by the root user. It should be secured accordingly. Use chmod so that the file can only be read by the owner and use chown to make root the owner, as shown in the following example:

$ chmod 400 your-app.conf
$ sudo chown root:root your-app.conf

62.2.2 Installation as a `systemd` Service

systemd is the successor of the System V init system and is now being used by many modern Linux distributions. Although you can continue to use init.d scripts with systemd, it is also possible to launch Spring Boot applications by using systemd ‘service’ scripts.

Assuming that you have a Spring Boot application installed in /var/myapp, to install a Spring Boot application as a systemd service, create a script named myapp.service and place it in /etc/systemd/system directory. The following script offers an example:

[Unit]
Description=myapp
After=syslog.target

[Service]
User=myapp
ExecStart=/var/myapp/myapp.jar
SuccessExitStatus=143

[Install]
WantedBy=multi-user.target

	Important
	Remember to change the `Description`, `User`, and `ExecStart` fields for your application.

	Note
	The `ExecStart` field does not declare the script action command, which means that the `run` command is used by default.

Note that, unlike when running as an init.d service, the user that runs the application, the PID file, and the console log file are managed by systemd itself and therefore must be configured by using appropriate fields in the ‘service’ script. Consult the service unit configuration man page for more details.

To flag the application to start automatically on system boot, use the following command:

$ systemctl enable myapp.service

Refer to man systemctl for more details.

62.2.3 Customizing the Startup Script

The default embedded startup script written by the Maven or Gradle plugin can be customized in a number of ways. For most people, using the default script along with a few customizations is usually enough. If you find you cannot customize something that you need to, use the embeddedLaunchScript option to write your own file entirely.

Customizing the Start Script when It Is Written

It often makes sense to customize elements of the start script as it is written into the jar file. For example, init.d scripts can provide a “description”. Since you know the description up front (and it need not change), you may as well provide it when the jar is generated.

To customize written elements, use the embeddedLaunchScriptProperties option of the Spring Boot Maven plugin or the properties property of the Spring Boot Gradle plugin’s launchScript.

The following property substitutions are supported with the default script:

Name	Description
`mode`	The script mode. Defaults to `auto`.
`initInfoProvides`	The `Provides` section of “INIT INFO”. Defaults to `spring-boot-application` for Gradle and to `${project.artifactId}` for Maven.
`initInfoRequiredStart`	The `Required-Start` section of “INIT INFO”. Defaults to `$remote_fs $syslog $network`.
`initInfoRequiredStop`	The `Required-Stop` section of “INIT INFO”. Defaults to `$remote_fs $syslog $network`.
`initInfoDefaultStart`	The `Default-Start` section of “INIT INFO”. Defaults to `2 3 4 5`.
`initInfoDefaultStop`	The `Default-Stop` section of “INIT INFO”. Defaults to `0 1 6`.
`initInfoShortDescription`	The `Short-Description` section of “INIT INFO”. Defaults to `Spring Boot Application` for Gradle and to `${project.name}` for Maven.
`initInfoDescription`	The `Description` section of “INIT INFO”. Defaults to `Spring Boot Application` for Gradle and to `${project.description}` (falling back to `${project.name}`) for Maven.
`initInfoChkconfig`	The `chkconfig` section of “INIT INFO”. Defaults to `2345 99 01`.
`confFolder`	The default value for `CONF_FOLDER`. Defaults to the folder containing the jar.
`inlinedConfScript`	Reference to a file script that should be inlined in the default launch script. This can be used to set environmental variables such as `JAVA_OPTS` before any external config files are loaded.
`logFolder`	The default value for `LOG_FOLDER`. Only valid for an `init.d` service.
`logFilename`	The default value for `LOG_FILENAME`. Only valid for an `init.d` service.
`pidFolder`	The default value for `PID_FOLDER`. Only valid for an `init.d` service.
`pidFilename`	The default value for the name of the PID file in `PID_FOLDER`. Only valid for an `init.d` service.
`useStartStopDaemon`	Whether the `start-stop-daemon` command, when it’s available, should be used to control the process. Defaults to `true`.
`stopWaitTime`	The default value for `STOP_WAIT_TIME`. Only valid for an `init.d` service. Defaults to 60 seconds.

Customizing a Script When It Runs

For items of the script that need to be customized after the jar has been written, you can use environment variables or a config file.

The following environment properties are supported with the default script:

Variable	Description
`MODE`	The “mode” of operation. The default depends on the way the jar was built but is usually `auto` (meaning it tries to guess if it is an init script by checking if it is a symlink in a directory called `init.d`). You can explicitly set it to `service` so that the `stop\|start\|status\|restart` commands work or to `run` if you want to run the script in the foreground.
`USE_START_STOP_DAEMON`	Whether the `start-stop-daemon` command, when it’s available, should be used to control the process. Defaults to `true`.
`PID_FOLDER`	The root name of the pid folder (`/var/run` by default).
`LOG_FOLDER`	The name of the folder in which to put log files (`/var/log` by default).
`CONF_FOLDER`	The name of the folder from which to read .conf files (same folder as jar-file by default).
`LOG_FILENAME`	The name of the log file in the `LOG_FOLDER` (`<appname>.log` by default).
`APP_NAME`	The name of the app. If the jar is run from a symlink, the script guesses the app name. If it is not a symlink or you want to explicitly set the app name, this can be useful.
`RUN_ARGS`	The arguments to pass to the program (the Spring Boot app).
`JAVA_HOME`	The location of the `java` executable is discovered by using the `PATH` by default, but you can set it explicitly if there is an executable file at `$JAVA_HOME/bin/java`.
`JAVA_OPTS`	Options that are passed to the JVM when it is launched.
`JARFILE`	The explicit location of the jar file, in case the script is being used to launch a jar that it is not actually embedded.
`DEBUG`	If not empty, sets the `-x` flag on the shell process, making it easy to see the logic in the script.
`STOP_WAIT_TIME`	The time in seconds to wait when stopping the application before forcing a shutdown (`60` by default).

	Note
	The `PID_FOLDER`, `LOG_FOLDER`, and `LOG_FILENAME` variables are only valid for an `init.d` service. For `systemd`, the equivalent customizations are made by using the ‘service’ script. See the service unit configuration man page for more details.

With the exception of JARFILE and APP_NAME, the settings listed in the preceding section can be configured by using a .conf file. The file is expected to be next to the jar file and have the same name but suffixed with .conf rather than .jar. For example, a jar named /var/myapp/myapp.jar uses the configuration file named /var/myapp/myapp.conf, as shown in the following example:

myapp.conf.

JAVA_OPTS=-Xmx1024M
LOG_FOLDER=/custom/log/folder

	Tip
	If you do not like having the config file next to the jar file, you can set a `CONF_FOLDER` environment variable to customize the location of the config file.

To learn about securing this file appropriately, see the guidelines for securing an init.d service.

62.3 Microsoft Windows Services

A Spring Boot application can be started as a Windows service by using winsw.

A (separately maintained sample) describes step-by-step how you can create a Windows service for your Spring Boot application.

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