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Runtime Environment

bpm is explicit about the interface that it provides to your job. If there is anything in this specification which is unclear or non-specific then please let us know so that we can be explicit about the interface and guarantees provided.

Lifecycle

Your process is started and has an unlimited amount of time to start up. You should use a post-start script and a health check if you want your job to only say it has completed deploying after it has started up. You do not need to manage any PID files yourself.

On shutdown your job will receive a SIGTERM. You then have 20 seconds to shutdown your application before it will be sent SIGQUIT to dump the stack (this is default behavior in the Go and Java runtimes) before being forcibly terminated.

If you require longer than this then you should use a drain script for your server. The drain script should put your server in such a state that it can shutdown within 15 seconds. It is acceptable and supported to terminate your process while running the drain script.

Environment Variables

Name Value
TMPDIR /var/vcap/data/JOB/tmp

Logging

Your process should write logs to standard output and standard error file descriptors. This data will be written to /var/vcap/sys/log/JOB/PROCESS.stdout.log and /var/vcap/sys/log/JOB/PROCESS.stderr.log respectively.

Any other files which are written to /var/vcap/sys/log/JOB inside the container will be written to /var/vcap/sys/log/JOB in the host system.

Resource Limits

bpm can enforce various resource limits on your processes. There are currently 3 different types: memory, open files, and processes.

Memory

If your process tries to allocate more memory that your configuration allows then it will be immediately killed by the OOM killer. This setting is more useful for agent jobs which do not use more memory under user load and do not want to affect the more important user-facing processes.

Open Files

The open files setting sets a limit on the number of open files (including network connections) which your job is allowed to have open at once. This is equivalent to setting ulimit -n for your process.

Processes

This setting places a limit on the number of PIDs which your process is allowed to create. This is to protect against fork-bombs and other resource exhaustion mistakes or attacks. Threads also count towards this limit as they are also given PIDs.

Storing Data

Temporary Files

Applications may store temporary files in either /tmp or /var/vcap/data/JOB/tmp (as per the BOSH recommendation). Both paths, and /var/tmp are mapped onto the same host volume (/var/vcap/data/JOB/tmp) and changes made to one will instantly appear in the other.

bpm will set the TMPDIR environment variable when executing your job to one of the paths listed above. This environment variable is respected by the majority of in-use standard libraries used by Cloud Foundry.

Note: Per the BOSH team's guidance the temporary filesystem is not mounted as tmpfs.

Ephemeral Data

You should store ephemeral data in /var/vcap/data/JOB. There are no guarantees that this data will be present in a different invocation of your job. The lifecycle of this data is tied with the underlying BOSH stemcell.

This storage area is useful for cached data that can be re-created by other means when necessary.

This storage area is shared between all processes in your job. It is your responsibility to make sure that the data saved by each of your job's processes does not collide.

Persistent Data

When the path /var/vcap/store exists bpm will mount the path /var/vcap/store/JOB into the job filesystem. As with /var/vcap/data/JOB bpm will create the leaf directory if it does not exist.

NOTE: Because persistent data access defaults to /var/vcap/store/JOB, job name changes will cause persistent data to no longer be accessible. When changing the name of a job the BOSH pre-start script should idempotently move the persistent data from /var/vcap/store/OLD-JOB to /var/vcap/store/NEW-JOB.

Shared Data

Note: This feature has been added to enable support for older jobs which use the file system to communicate with other jobs. It is preferable in nearly all cases to use the network to communicate across job boundaries. Using the network reduces scheduling constraints such that a job can be un-collocated and allows more modern access control (key rotation, etc.) of the information being transferred between your jobs.

If your job configuration lists shared volumes (additional_volumes: key) then these paths will be created if they do not exist before being mounted into the job filesystem. These volumes will be mounted read-write. All collocated jobs which list a particular volume path will be given a volume they can all share.

Only volume paths inside the /var/vcap/data, and (when present) the /var/vcap/store directories are currently permitted. Specifying paths which are not inside this directory will cause the job to fail to start.

monit Workarounds

There are various monit quirks that bpm attempts to hide or smooth over.

Instant Restart

If an operator runs monit stop JOB && monit start JOB then monit will wait until the monitored process has completely stopped and the stop program listed in the configuration has completely finished before attempting to start the job again. This is unsurprising behavior.

Unfortunately monit restart does not wait until the existing job has stopped before starting the same job again. As soon as the existing job has removed its PID file monit forks and starts the new process. This behavior is unexpected, subtle, and full of race conditions. A considerable number of BOSH releases are unknowingly suffering from bugs caused by this.

bpm enforces its own locking around process operations to avoid these race conditions. It is completely safe (from a correctness perspective, you may still break your service) to run monit restart on a job which uses bpm.