Add opt-in for file name

[gberche-orange]

As a syslog-release release user
In order to filter syslog entries in a similar way than

• bosh ssh <instance-group>/<index>
• tail -f /var/vcap/jobs/<job>/<file-name>.log
  I need syslog release to issue the file-name in addition to instance id

[ctlong]

❓ Why do you need to filter syslog messages by filename? Can you give an example of why you want this?

Most jobs only log to /var/vcap/jobs/<job>/<job>.stdout.log or /var/vcap/jobs/<job>/<job>.stderr.log so I confess this has not been a pain point for me. Usually it is enough to know what job the log line originates from.

[gberche-orange]

Our k3s bosh release emits more verbose k8s audit logs into a distinct audit.log file

https://github.com/orange-cloudfoundry/k3s-wrapper-boshrelease/blob/585b1737714c1a4b907f3e598a796f8ae1a29257/jobs/k3s-server/templates/bin/ctl.erb#L186

export FLAGS="$FLAGS --kube-apiserver-arg=audit-log-path=/var/vcap/sys/log/k3s-server/audit.log"

The ability to filter by log file names would enable choosing whether or not to display these log lines.

See https://kubernetes.io/docs/tasks/debug/debug-cluster/audit/#log-backend for more details about the rationale for emitting this logs lines into a distinct file (and not stdout/stderr which are in the case of this release the k3s binary)

[ctlong]

Ok, I'm convinced. This feature makes sense as an opt-in to me.

To add it, you'll need to PR to both this repo and https://github.com/cloudfoundry/blackbox. The top-level BOSH property feature flag will be in this repo. The blackbox repo is the code that actually reads log lines and forwards them to syslog, so that code would need to be altered to include an opt-in for recording the file name as well.