Cloud Foundry Command Line Java plugin

This plugin for the Cloud Foundry Command Line provides convenience utilities to work with Java applications deployed on Cloud Foundry.

Currently, it allows to:

• Trigger and retrieve a heap dump from an instance of a Cloud Foundry Java application
• Trigger and retrieve a thread dump from an instance of a Cloud Foundry Java application

Installation

Installation via CF Community Repository

Make sure you have the CF Community plugin repository configured or add it via (cf add-plugin-repo CF-Community http://plugins.cloudfoundry.org)

Trigger installation of the plugin via

cf install-plugin -r CF-Community "java"

Manual Installation

Download the binary file for your target OS from the latest release.

If you've already installed the plugin and are updating it, you must first execute the cf uninstall-plugin java command.

Install the plugin with cf install-plugin [cf-cli-java-plugin] (replace [cf-cli-java-plugin] with the actual binary name you will use, which depends on the OS you are running).

You can verify that the plugin is successfully installed by looking for java in the output of cf plugins.

Updating from version 1.x to 2.x

With release 2.0 we aligned the convention of the plugin having the same name as the command it contributes (in our case, java). This change mostly affects you in the way you update your plugin. If you have the version 1.x installed, you will need to uninstall the old version first by using the command: cf uninstall-plugin JavaPlugin. You know you have the version 1.x installed if JavaPlugin appears in the output of cf plugins.

Permission Issues

On Linux and macOS, if you get a permission error, run chmod +x [cf-cli-java-plugin] (replace [cf-cli-java-plugin] with the actual binary name you will use, which depends on the OS you are running) on the plugin binary. On Windows, the plugin will refuse to install unless the binary has the .exe file extension.

Usage

Prerequisites

JDK Tools

This plugin internally uses jmap for OpenJDK-like Java virtual machines. When using the Cloud Foundry Java Buildpack, jmap is no longer shipped by default in order to meet the legal obligations of the Cloud Foundry Foundation. To ensure that jmap is available in the container of your application, you have to explicitly request a full JDK in your application manifest via the JBP_CONFIG_OPEN_JDK_JRE environment variable. This could be done like this:

---
applications:
- name: <APP_NAME>
  memory: 1G
  path: <PATH_TO_BUILD_ARTIFACT>
  buildpack: https://github.com/cloudfoundry/java-buildpack
  env:
    JBP_CONFIG_OPEN_JDK_JRE: '{ jre: { repository_root: "https://java-buildpack.cloudfoundry.org/openjdk-jdk/bionic/x86_64", version: 11.+ } }'

Please note that this requires the use of an online buildpack (configured in the buildpack property). When system buildpacks are used, staging will fail with cache issues, because the system buildpacks don’t have the JDK chached. Please also note that this is not to be considered a recommendation to use a full JDK. It's just one option to get the tools required for the use of this plugin when you need it, e.g., for troubleshooting. The version property is optional and can be used to request a specific Java version.

SSH Access

As it is built directly on cf ssh, the cf java plugin can work only with Cloud Foundry applications that have cf ssh enabled. To check if your app fulfills the requirements, you can find out by running the cf ssh-enabled [app-name] command. If not enabled yet, run cf enable-ssh [app-name].

Note: You must restart your app after enabling SSH access.

In case a proxy server is used, ensure that cf ssh is configured accordingly. Refer to the official documentation of the Cloud Foundry Command Line for more information. If cf java is having issues connecting to your app, chances are the problem is in the networking issues encountered by cf ssh. To verify, run your cf java command in "dry-run" mode by adding the -n flag and try to execute the command line that cf java gives you back. If it fails, the issue is not in cf java, but in whatever makes cf ssh fail.

Commands

NAME:
   java - Obtain a heap dump or thread dump from a running, SSH-enabled Java application

USAGE:
   cf java [heap-dump|thread-dump] APP_NAME

OPTIONS:
   -app-instance-index       -i [index], select to which instance of the app to connect
   -dry-run                  -n, just output to command line what would be executed
   -keep                     -k, keep the heap dump in the container; by default the heap dump will be deleted from the container's filesystem after been downloaded
   -container-dir            -cd, the directory path in the container that the heap dump file will be saved to
   -local-dir                -ld, the local directory path that the dump file will be saved to

The heap dump will be copied to a local file if -local-dir is specified as a full folder path. Without providing -local-dir the heap dump will only be created in the container and not transferred. To save disk space of the application container, heap dumps are automatically deleted unless the -keep option is set.

Providing -container-dir is optional. If specified the plugin will create the heap dump at the given file path in the application container. Without providing this parameter, the heap dump will be created either at /tmp or at the file path of a file system service if attached to the container.

cf java heap-dump [my-app] -local-dir /local/path [-container-dir /var/fspath]

The thread dump will be outputted to std-out. You may want to redirect the command's output to file, e.g., by executing:

cf java thread-dump [my_app] -i [my_instance_index] > heap-dump.hprof

The -k flag is invalid when invoking cf java thread-dump. (Unlike with heap dumps, the JVM does not need to output the thread dump to file before streaming it out.)

Limitations

The capability of creating heap dumps is also limited by the filesystem available to the container. The cf java heap-dump command triggers the heap dump to file system, read the content of the file over the SSH connection, and then remove the heap dump file from the container's file system (unless you have the -k flag set). The amount of filesystem space available to a container is set for the entire Cloud Foundry landscape with a global configuration. The size of a heap dump is roughly linear with the allocated memory of the heap. So, it could be that, in case of large heaps or the filesystem having too much stuff in it, there is not enough space on the filesystem for creating the heap dump. In that case, the creation of the heap dump and thus the command will fail.

From the perspective of integration in workflows and overall shell-friendliness, the cf java plugin suffers from some shortcomings in the current cf-cli plugin framework:

• There is no distinction between stdout and stderr output from the underlying cf ssh command (see this issue on the cf-cli project)
  • The cf java will however exit with status code 1 when the underpinning cf ssh command fails
  • If split between stdout and stderr is needed, you can run the cf java plugin in dry-run mode (--dry-run flag) and execute its output instead
• The plugin is not current capability of storing output directly to file (see this issue on the cf-cli project)
  • The upstream change needed to fix this issue has been scheduled at Pivotal; when they provide the new API we need, we'll update the cf java command to save output to file.

Side-effects on the running instance

Executing a thread dump via the cf java command does not have much of an overhead on the affected JVM. (Unless you have a lot of threads, that is.)

Heap dumps, on the other hand, have to be treated with a little more care. First of all, triggering the heap dump of a JVM makes the latter execute in most cases a full garbage collection, which will cause your JVM to become unresponsive for the duration. How much time is needed to execute the heap dump, depends on the size of the heap (the bigger, the slower), the algorithm used and, above all, whether your container is swapping memory to disk or not (swap is bad for the JVM). Since Cloud Foundry allows for over-commit in its cells, it is possible that a container would begin swapping when executing a full garbage collection. (To be fair, it could be swapping even before the garbage collection begins, but let's not knit-pick here.) So, it is theoretically possible that execuing a heap dump on a JVM in poor status of health will make it go even worse.

Secondly, as the JVMs output heap dumps to the filesystem, creating a heap dump may lead to to not enough space on the filesystem been available for other tasks (e.g., temp files). In that case, the application in the container may suffer unexpected errors.

Tests and Mocking

The tests are written using Ginkgo with Gomega for the BDD structure, and Counterfeiter for the mocking generation. Unless modifications to the helper interfaces cmd.CommandExecutor and uuid.UUIDGenerator are needed, there should be no need to regenerate the mocks.

To run the tests, go to the root of the repository and simply run gingko (you may need to install Ginkgo first, e.g., go get github.com/onsi/ginkgo/ginkgo puts the executable under $GOPATH/bin).