|
1 | | -# cf-cli-java-plugin |
2 | | -Plugin for the Cloud Foundry CLI that adds tools to troubleshoot CF Java apps |
| 1 | +# Cloud Foundry Command Line Java plugin |
| 2 | + |
| 3 | +This plugin for the [Cloud Foundry Command Line](https://github.com/cloudfoundry/cli) provides convenience utilities to work with Java applications deployed on Cloud Foundry. |
| 4 | + |
| 5 | +Currently, it allows to: |
| 6 | +* Trigger and retrieve a heap-dump from an instance of a Cloud Foundry Java application |
| 7 | +* Trigger and retrieve a thread-dump from an instance of a Cloud Foundry Java application |
| 8 | + |
| 9 | +## Installation |
| 10 | + |
| 11 | +Download the binary file for your target OS from the [latest release](https://github.com/SAP/cf-cli-java-plugin/releases/latest). |
| 12 | + |
| 13 | +If you've already installed the plugin and are updating it, you must first execute the `cf uninstall-plugin JavaPlugin` command. |
| 14 | + |
| 15 | +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). |
| 16 | + |
| 17 | +You can verify that the plugin is successfully installed by looking for `JavaPlugin` in the output of `cf plugins`. |
| 18 | + |
| 19 | +### Permission Issues |
| 20 | + |
| 21 | +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. |
| 22 | +On Windows, the plugin will refuse to install unless the binary has the `.exe` file extension. |
| 23 | + |
| 24 | +## Usage |
| 25 | + |
| 26 | +<pre> |
| 27 | +NAME: |
| 28 | + java - Obtain a heap-dump or thread-dump from a running, Diego-enabled, SSH-enabled Java application |
| 29 | + |
| 30 | +USAGE: |
| 31 | + cf java [heap-dump|thread-dump] APP_NAME |
| 32 | + |
| 33 | +OPTIONS: |
| 34 | + -app-instance-index -i [index], select to which instance of the app to connect |
| 35 | + -dry-run -n, just output to command line what would be executed |
| 36 | + -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 |
| 37 | +</pre> |
| 38 | + |
| 39 | +The heap-dump or thread-dump (depending on what you execute) will be outputted to `std-out`. |
| 40 | +You may want to redirect the command's output to file, e.g., by executing: |
| 41 | +`cf java heap-dump [my_app] -i [my_instance_index] > heap-dump.hprof` |
| 42 | + |
| 43 | +The `-k` flag is invalid when invoking `cf java thread-dump`. |
| 44 | +(Unlike with heap-dumps, the JVM does not need to output the threaddump to file before streaming it out.) |
| 45 | + |
| 46 | +## Limitations |
| 47 | + |
| 48 | +As it is built directly on `cf ssh`, the `cf java` plugin can work only with Diego applications that have `cf ssh` enabled. |
| 49 | +To check if your app fulfills the requirements, you can find out by running the `cf ssh-enabled [app-name]` command. |
| 50 | + |
| 51 | +Also, `cf ssh` is *very* picky with proxies. |
| 52 | +If `cf java` is having issues connecting to your app, chances are the problem is in the networking issues encountered by `cf ssh`. |
| 53 | +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. |
| 54 | +If it fails, the issue is not in `cf java`, but in whatever makes `cf ssh` fail. |
| 55 | + |
| 56 | +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: |
| 57 | +* There is no distinction between `stdout` and `stderr` output from the underlying `cf ssh` command (see [this issue on the `cf-cli` project](https://github.com/cloudfoundry/cli/issues/1074)) |
| 58 | + * The `cf java` will however exit with status code `1` when the underpinning `cf ssh` command fails |
| 59 | + * 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 |
| 60 | +* The plugin is not current capability of storing output directly to file (see [this issue on the `cf-cli` project](https://github.com/cloudfoundry/cli/issues/1069)) |
| 61 | + * 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. |
| 62 | + |
| 63 | +## Side-effects on the running instance |
| 64 | + |
| 65 | +Executing a thread-dump via the `cf java` command does not have much of an overhead on the affected JVM. |
| 66 | +(Unless you have **a lot** of threads, that is.) |
| 67 | + |
| 68 | +Heap-dumps, on the other hand, have to be treated with a little more care. |
| 69 | +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. |
| 70 | +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). |
| 71 | +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. |
| 72 | +(To be fair, it could be swapping even *before* the garbage collection begins, but let's not knit-pick here.) |
| 73 | +So, it is theoretically possible that execuing a heap dump on a JVM in poor status of health will make it go even worse. |
| 74 | + |
| 75 | +Secondly, JVMs output heap dumps to the filesystem. |
| 76 | +What the `cf java heap-dump` command does it, quite literally, trigger 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). |
| 77 | +The amount of filesystem space available to a container is set for the entire Cloud Foundry landscape with a global configuration. |
| 78 | +The size of a heap dump is linear with the size of the heap. |
| 79 | +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. |
| 80 | +In that case, the command will likely fail in a rather unpredictable fashion. |
| 81 | + |
| 82 | +## Tests and Mocking |
| 83 | + |
| 84 | +The tests are written using [Ginkgo](https://onsi.github.io/ginkgo/) and [Gomega](https://onsi.github.io/gomega/) for the BDD structure, and [Counterfeit](https://github.com/maxbrunsfeld/counterfeiter) for the mocking generation. |
| 85 | +Unless modifications are needed to the helper interfaces `cmd.CommandExecutor` and `uuid.UUIDGenerator` are needed, there should be no need to regenerate the mocks. |
| 86 | + |
| 87 | +To run the tests, go to the root of the repository and simply run `gingko` (you may need to install the package, e.g., `sudo apt install golang-ginkgo-dev` on Ubuntu). |
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