Name: exemplar-release
Owner: Cloud Foundry
Description: null
Created: 2017-03-03 01:37:50.0
Updated: 2018-05-13 04:00:19.0
Pushed: 2018-05-23 18:32:51.0
Homepage: null
Size: 30
Language: Shell
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This exemplar BOSH release is intended as a collection of recommended practices for authoring a BOSH release, with a particular focus on jobs. Not all advice here should be taken verbatim for all releases, so we have made an attempt to explain the reasoning behind all recommendations so that the conscientious release author can adapt the recommendations to their unique circumstances.
tee and logger ApproachThe primary goals of a BOSH job are to maximize availability, remove the need for manual operation, and contribute to quick deployments. To accomplish this, it is important to understand the BOSH deployment lifecycle and what your job should be doing to take advantage of it.
A process should be able to start and stay running without dependencies being ready. Only once its required dependencies (those needed to respond to requests) are reporting as healthy should it report as healthy. This allows jobs to be started in any order and then propagate health upwards through their dependents when they're ready. We think removing this burden of job ordering from the operator reduces complexity and increases system reliability.
On the other hand, stopping can follow a similar but reversed pattern. If your service is being load-balanced then you can use a signal in your drain script to mark yourself as unhealthy. After a period of time or after no more requests are detected you can stop the process completely. If you aren't behind a load balancer then you will have to find another way to tell upstream components about your imminent demise.
Every BOSH job goes through a specific lifecycle for starting and stopping. The BOSH website has a great overview of the lifecycle. You may wish to review this before reading on to our recommendations for the individual parts of the lifecycle.
Pre-start scripts are run before BOSH hands off control to Monit, so will not necessarily run every time a job starts
(e.g. if a VM is rebooted outside of BOSH's control). However, pre-start scripts will run at least once for every new
release version that is deployed, and have no timeout (in contrast to a start script). Therefore, pre-start scripts
can best be used for performing lengthy set-up of persistent state that must be done for a new version of a release,
such as database migrations. However, because the pre-start script does not necessarily run in every VM your job
will run in, do not perform any work in temporary directories such as /var/vcap/sys/run (see VM Configuration Locations for the list of temporary directories).
In general, a pre-start script should not be necessary and the start script should be sufficient. If you find a pre-start script is necessary, keep the above caveats in mind.
The start script has two main responsibilities: writing the process ID (PID) to a pidfile and starting the main process. All setup required for the process to run (that has not been done in the pre-start script) must be done at this time. Monit places a short timeout on the pidfile being written, so the work done in the start script should be focused on executing your process and getting it healthy quickly.
Note: This script will likely run many times, so ensure that it is idempotent (that it can be run repeatedly without causing the system to enter a bad state)
The general workflow of a start script:
Create a log directory for log persistence in /var/vcap/sys/log/<job name>
Idempotency recommendation: Do not fail if the log directory already exists
Create a run directory to contain the pidfile in /var/vcap/sys/run/<job name>
Idempotency recommendation: Do not fail if the run directory already exists
Change ownership permissions on the log and run directories to user vcap and group vcap
Run your process with start-stop-daemon, which will manage your process's pidfile, ensuring multiple instances
of the process are not run simultaneously. A recommended usage of start-stop-daemon looks like this:
n/start-stop-daemon \
rite the pidfile, and error if it exists
nd refers to an already-running process
idfile "$PIDFILE" \
ake-pidfile \
un the process as the less-privileged vcap user
huid vcap:vcap \
tart the given process and redirect its logs
tart \
xec /var/vcap/packages/paragon/bin/web \
>> "$LOG_DIR/web.out.log" \
>> "$LOG_DIR/web.err.log"
Refer to the start script of the pararagon job for a more-complete example.
Note: The start script is executed as root. Do not assume you can only break your own process.
Note: If your process cannot start quickly, consider moving long-running tasks to pre-start or post-start.
Note for Windows Releases: The Windows BOSH Agent does not use monit and manages starting the script directly. If
your pre-start and post-start scripts have been written following the guidance in this
document, the Agent will be able to start your process correctly.
Job logs should be put in the /var/vcap/sys/log/<job> directory. You can redirect the logs from your server (if
they're output on stdout and stderr) by using standard redirection:
... \
"/var/vcap/sys/log/<job>/<process>.out.log" \
> "/var/vcap/sys/log/<job>/<process>.err.log"
If your process takes log locations as parameters, use that instead:
... \
out-log-file "/var/vcap/sys/log/<job>/<process>.out.log" \
err-log-file "/var/vcap/sys/log/<job>/<process>.err.log"
For detail on forwarding logs to external locations, please see Exporting Logs.
Post-start is useful for custom health-checks to ensure you job has started correctly. For example, if your process starts quickly, but takes time to discover services or connect to its backend, you may wish to use post-start to query the readiness of your job to start handling requests. If a post-start script is provided, BOSH will not consider a job to be ready until it has exited successfully.
The authors have never seen this used. It may be useful for checking the health of an entire deployment. If you find it useful, please let us know.
Job is unmonitored before any stop scripts can run, so you can safely exit in either drain or monit stop without the
job becoming listed as unhealthy.
Drain scripts are optional hooks into the BOSH job lifecycle that are run before stopping the job via Monit. They
are typically used for services which must perform some work before being shut down, for example flushing a request
queue or evacuating containers from a Diego cell. As a rule of thumb, if monit stopping your job could cause dropped
connections or a lack of availability, a drain script should be used to prevent this. Most commonly, your drain script
will send a request to a drain endpoint on your process and wait for it to return rather than implementing the drain
behavior itself.
A concrete example is the gorouter, which has a configurable drain_wait parameter. When non-zero,
gorouter's drain script will instruct gorouter to report itself as unhealthy to its load-balancer with the intent of
being removed from the balanced instance group before shutting down and rejecting requests. When monit stop is called,
the router will already be receiving no connections, so will not drop connections when it is shut down quickly. This is
the lame duck pattern.
Drain scripts have no timeout, so should take whatever time necessary to block on any draining work. One may, however, run the risk of writing a drain script that never finishes and blocks a deployment. A well-written drain script is guaranteed to finish, such as by adding your own sensible timeout around draining work (e.g. 10 minutes).
When your draining process has completed, your drain script should output a “0” to STDOUT to inform BOSH that draining is complete.
Open question: If your job needs to wait for another job to drain first, what is the best way to block on that? If you have any ideas, please let us know.
The stop program in your job's monit file is executed after the drain script (if present) has finished running. It can
also be run directly by an operator if they execute monit stop <job> on the machine. By default, there is a 30 second
timeout on this script completing. Monit will assume scripts taking longer than this have failed. We do not recommend
changing this value if you need more time. Instead, you should do all the work necessary in your drain script such
that your service can shutdown quickly (where “quickly” generally means in under 10 seconds).
If you're not using drain then we recommend that you send SIGTERM to your process which should cause it to start
shutting down. If your process shuts down at this point then you're good to go. If for some reason your process locks up
or is unable to exit for some other reason then you should send SIGKILL before the timeout. If your language runtime
supports dumping the stacks of all running threads on SIGQUIT (Go and Java do) then you can send that signal just
before the SIGKILL to aid debugging why the process is stuck. If you are not using a SIGKILL respecting runtime then
adding this functionality to your own program normally isn't difficult.
start-stop-daemon can be used for this:
n/start-stop-daemon \
Remove the pidfile after killing the process
pidfile "$PIDFILE" \
remove-pidfile \
Send SIGTERM, wait for the process to die for 20 seconds
If the process has not died, send SIGQUIT and wait for 1 second
If the process has still not died, send SIGKILL
retry TERM/20/QUIT/1/KILL \
If the process is already gone, do not error
oknodo \
stop
Refer to the stop script of the pararagon job for a more-complete example.
If you're using drain to kill the process then your process may already be shut down by the time that monit stop is
called. In this case we do not need to do anything further in the stop executable.
Note for Windows Releases: The Windows BOSH Agent does not use monit and manages starting the script directly. If
your pre-start and post-start scripts have been written following the guidance in this
document, the Agent will be able to stop your process correctly.
The properties you include in your spec file create the product surface for your job from the perspective of the operator component. Job properties can make it much easier or much harder to operate a deployment, so one should be mindful of the operator when making decisions about properties.
my-job.port, my-job.hostname), but should
only use namespace to create property groups that the job cares about (e.g. database.* and blobstore.*).Links allow jobs to provide and consume configuration that needs to be shared between jobs, which can greatly reduce the amount of configuration required in a deployment manifest. Instead, jobs can declare which information they need and BOSH will provide that information automatically. When links are used correctly, there are two main benefits:
If links are used whenever a job depends on configuration from another job, manifests can become much simpler and deployments can become more reliable. When authoring your release, all properties you include in your spec file should change the runtime behavior of your process and should not include IP addresses, domain names, credentials, or certificates of other jobs. If you are including these properties, they are candidates for links instead. If the job you depend on does not provide the information as a link, please consider submitting an issue or PR to the maintainer.
Sometimes it is necessary to allow operators to override individual properties within a link. For example, if your job uses a link's IP information to find a dependent service, but a particular deployment may be using custom DNS for service discovery, your job template could prefer the DNS property over the link. That template could look like this:
rver = nil
_p("database_location") do |prop|>
server = prop
d.else do
server = link("database").instances[0].address
d
er: <%= server %>
Any template in your job can use ERB (even the monit files!). While this is extremely powerful it can be very difficult to understand and maintain complex templates. Therefore, we advise avoiding any ERB in your control scripts wherever possible. The control flow of starting and stopping your program should be deterministic and simple. All ERB should be relegated to static configuration files so that properties can be interpolated.
Your templates should be simple enough to not need testing, such as by doing a simple passthrough to property parsing
in your own code, but you may find yourself with more-complex templating needs, such as when writing a release wrapping
third-party code. Unfortunately, it is difficult to test BOSH template rendering. It is preferable to have a simple
template (e.g. <% p('my-properties').to_json %>) that you transform with a custom executable that you can test
in your standard unit-testing workflow.
The ShellCheck tool can be used to find common errors in your bash scripts. This yet another reason to
keep ERB out of your scripts!
Try to keep your Monit configuration as simple as possible. The BOSH team is planning on removing Monit soon - do not couple yourself to it! This includes such changes as monitoring memory and changing away from the default timeout.
You must specify group vcap in your monit file because the agent uses this tag to find
processes it should be managing on the machine.
BOSH itself does not handle forwarding logs off-system. If you have written your logs appropriately as described in the Logging section, operators can choose the correct log-forwarding mechanism for their deployment using job co-location in the deployment manifest or BOSH addons. Operators may choose to use something like google-fluentd or syslog-release. If you are also responsible for providing a deployment manifest generation tool, you may wish to provide the option to add syslog-release forwarding to all components.
Backwards Compatibility Warning: If your release is currently responsible for forwarding logs off-system, by following this guide and removing that functionality, you are putting the onus for logging on deployment authors (e.g. cf-deployment or your local friendly closed-source proprietary offering) to configure logging. If your release has traditionally done this, deployment authors may not know to update the deployment and logs could be lost. If you are removing this functionality, please coordinate appropriately with deployment authors and operators.
metron_agent has functionality to forward syslogs, but this has been superseded by syslog-release. metron_agent
should only be used to forward logs to loggregator.
tee and logger ApproachMany releases currently include complex setup to forward logs to both /var/vcap/sys/log as well as syslog. This
is not necessary if operators use one of the log-forwarding options mentioned above. Drawbacks of the tee and logger
approach include starting multiple processes for every line of logs, fairly subtle behavior that can easily break or
security vulnerabilities. If your release has any code like the following, please remove it and follow the
recommendations above:
OT USE THIS CODE
> \
tee -a >(logger -p user.info -t vcap.$(basename $0).stdout) | \
awk -W interactive '{ gsub(/\\n/, ""); system("echo -n [$(date +\"%Y-%m-%d %H:%M:%S%z\")]"); print " " $0 }' \
>> /var/vcap/sys/log/<job>/<process>.out.log
2> \
tee -a >(logger -p user.error -t vcap.$(basename $0).stderr) | \
awk -W interactive '{ gsub(/\\n/, ""); system("echo -n [$(date +\"%Y-%m-%d %H:%M:%S%z\")]"); print " " $0 }' \
>> /var/vcap/sys/log/<job>/<process>.err.log
OT USE THIS CODE
If you must use this, you should understand it. The exec calls redirect STDOUT and STDERR respectively,
sending them to a sub-shell that calls tee. tee splits the output to 1) syslog via logger and 2) the BOSH log
directory (but not before appending timestamps with awk).