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Changes to utilize default +UseContainerSupport in new releases of Java #47

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Changes to utilize default +UseContainerSupport in new releases of Java #47

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23 changes: 3 additions & 20 deletions images/alpine/openjdk8/jdk/README.md
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Expand Up @@ -96,10 +96,6 @@ The startup process is configured mostly via environment variables:
* **JAVA_APP_DIR** the directory where the application resides. All paths in your application are relative to this directory. By default it is the same directory where this startup script resides.
* **JAVA_LIB_DIR** directory holding the Java jar files as well an optional `classpath` file which holds the classpath. Either as a single line classpath (colon separated) or with jar files listed line-by-line. If not set **JAVA_LIB_DIR** is the same as **JAVA_APP_DIR**.
* **JAVA_OPTIONS** options to add when calling `java`
* **JAVA_MAJOR_VERSION** a number >= 7. If the version is set then only options suitable for this version are used. When set to 7 options known only to Java > 8 will be removed. For versions >= 10 no explicit memory limit is calculated since Java >= 10 has support for container limits.
* **JAVA_MAX_MEM_RATIO** is used when no `-Xmx` option is given in `JAVA_OPTIONS`. This is used to calculate a default maximal Heap Memory based on a containers restriction. If used in a Docker container without any memory constraints for the container then this option has no effect. If there is a memory constraint then `-Xmx` is set to a ratio of the container available memory as set here. The default is `25` when the maximum amount of memory available to the container is below 300M, `50` otherwise, which means in that case that 50% of the available memory is used as an upper boundary. You can skip this mechanism by setting this value to 0 in which case no `-Xmx` option is added.
* **JAVA_INIT_MEM_RATIO** is used when no `-Xms` option is given in `JAVA_OPTIONS`. This is used to calculate a default initial Heap Memory based on a containers restriction. If used in a Docker container without any memory constraints for the container then this option has no effect. If there is a memory constraint then `-Xms` is set to a ratio of the container available memory as set here. By default this value is not set.
* **JAVA_MAX_CORE** restrict manually the number of cores available which is used for calculating certain defaults like the number of garbage collector threads. If set to 0 no base JVM tuning based on the number of cores is performed.
* **JAVA_DIAGNOSTICS** set this to get some diagnostics information to standard out when things are happening
* **JAVA_MAIN_CLASS** A main class to use as argument for `java`. When this environment variable is given, all jar files in `$JAVA_APP_DIR` are added to the classpath as well as `$JAVA_LIB_DIR`.
* **JAVA_APP_JAR** A jar file with an appropriate manifest so that it can be started with `java -jar` if no `$JAVA_MAIN_CLASS` is set. In all cases this jar file is added to the classpath, too.
Expand Down Expand Up @@ -131,48 +127,35 @@ These variables can be also set in a shell config file `run-env.sh`, which will

This startup script also checks for a command `run-java-options`. If existent it will be called and the output is added to the environment variable `$JAVA_OPTIONS`.

The startup script also exposes some environment variables describing container limits which can be used by applications:

* **CONTAINER_CORE_LIMIT** a calculated core limit as described in https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt
* **CONTAINER_MAX_MEMORY** memory limit given to the container

Any arguments given to the script are given through directly as argument to the Java application.

Example:

```
# Set the application directory directly
export JAVA_APP_DIR=/deployments
# Set -Xmx based on container constraints
export JAVA_MAX_MEM_RATIO=40
# Start the jar in JAVA_APP_DIR with the given arguments
./run-java.sh --user maxmorlock --password secret
```

### Options

This script can also be used to calculate reasonable, best-practice options for starting Java apps in general. For example, when running Maven in a container it makes sense to respect container Memory constraints.

The subcommand `options` can be used to print options to standard output so that is can be easily used to feed it to another, Java based application.

When no extra arguments are given, all defaults will be used, which can be influenced with the environment variables described above.

You can select specific sets of options by providing additional arguments:

* `--debug` : Java debug options if `JAVA_DEBUG` is set
* `--memory` : Memory settings based on the environment variables given
* `--proxy` : Evaluate proxy environments variables
* `--cpu` : Tuning when the number of cores is limited
* `--gc` : GC tuning parameters
* `--jit` : JIT options
* `--diagnostics` : Print diagnostics options when `JAVA_DIAGNOSTICS` is set
* `--java-default` : Same as `--memory --jit --diagnostic --cpu --gc`
* `--java-default` : Default options

Example:

```
# Call Maven with the proper memory settings when running in an container
export MAVEN_OPTS="$(run-java.sh options --memory)"
# Call Maven with the proper proxy settings when running in an container
export MAVEN_OPTS="$(run-java.sh options --proxy)"
mvn clean install
```

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