Allow specifying alternate journal fields

[cyrus-mc]

PR for issue #1809.

This changes the semantics of field systemdFilter to allow specifying a journal field. If none is specified, the behavior reverts to the default of assuming _SYSTEMD_UNIT.

[pepov]

@cyrus-mc can you add a simple example to the PR description please?

[cyrus-mc]

@pepov Here you go

apiVersion: logging-extensions.banzaicloud.io/v1alpha1
kind: HostTailer
metadata:
  labels:
    app.kubernetes.io/name: systemd-hosttailer
  name: systemd
  namespace: logging
spec:
  systemdTailers:
  - maxEntries: 100
    name: kubelet
    systemdFilter: kubelet.service
  - maxEntries: 100
    name: kernel
    systemdFilter: SYSLOG_IDENTIFIER=kernel

Here I am creating a systemd tailer for the kubelet.service as well as kernel logs, which are logged under journal field SYSLOG_IDENTIFIER.

This will generate a container with arguments:

      - command:
        - /fluent-bit/bin/fluent-bit
        - -i
        - systemd
        - -p
        - path=/var/log/journal
        - -p
        - db=/var/pos/systemd-host-tailer-kernel.db
        - -p
        - max_entries=100
        - -p
        - systemd_filter=SYSLOG_IDENTIFIER=kernel
        - -o
        - file
        - -p
        - format=plain
        - -p
        - path=/dev/
        - -p
        - file=stdout

[pepov]

thanks @cyrus-mc !