Support CRI log format

[steven-sheehy]

Is your feature request related to a problem? Please describe.
Containerd does not support JSON format, so after setting promtail's entry_parser: raw to make it work, I noticed that there were duplicate timestamps in the loki output. Containerd writes its logs in the CRI format <RFC3339Nano> <stream> <flags> <app output>\n. Other CRI runtimes like CRI-O may also support this same format, but I am not sure. Example log:

2019-02-23T05:30:45.598142519Z stdout F INFO 2019-02-23 05:30:45,596 [main] c.f.e.w.i.InventoryApplication: No active profile set

When I view the logs in Grafana, containerd's timestamp and other metadata isn't removed and the loki timestamp differs slightly from the containerd timestamp.

Describe the solution you'd like
promtail should be able to retrieve logs from containerd with the correct timestamp and remove all other data except the application stdout.

Describe alternatives you've considered
Instead of a containerd-specific solution, implement a generic regex-basedEntryParser similar to Fluent Bit's regex parser.

Or, instead of reading log files integrate with containerd directly via their API. This is the approach containerd's dev recommended via slack.

Additional context
In Grafana, if I enable all options I end up with 4 date/times being printed on screen, making it unuseable:

1. Grafana timestamp
2. Grafana local time
3. Containerd timestamp
4. Application timestamp

This issue deals with only item 3 above.

Containerd is the underlying runtime of Docker 18.09+, the runtime used in IBM Cloud, Pivotal Cloud Foundry and soon to be GKE and Azure so it's important that it is supported.

[steven-sheehy]

I've confirmed with both containerd and CRI-O developers that they implement the CRI log format and that the format is stable. Updating title to reflect that.

[NickLarsenNZ]

I've confirmed with both containerd and CRI-O developers that they implement the CRI log format and that the format is stable. Updating title to reflect that.

For anyone stumbling on this issue, the archived link is: https://github.com/kubernetes/design-proposals-archive/blob/main/node/kubelet-cri-logging.md