README.md

authors	state
Josh Wilsdon <[email protected]>	publish

RFD 10 Sending GZ Docker Logs to Manta

Overview

With RFD 0002, we've added support for docker logging modes which for the most part leave log files in the:

/zones/<uuid>/logs/stdio.log

for each docker container. These files are accessible (with docker cli >= 1.9) for any log-driver except 'none' via the docker logs mechanism. We do not yet support the max-file or max-size options for the json-file driver. As it stands right now, without these changes, the GZ log file will continue to grow until it has exhausted the quota of the container's zoneroot filesystem.

Since these log files are not accessible to customers any way other than docker logs, they cannot rotate them. So currently they can grow until they fill the zoneroot quota of the container. If we just rotated them in place, customers would not be able to access them as docker logs only provides access to the most recent log. In order to deal with these problems, we wanted to instead rotate the logs to Manta so that customers could access all their logs (using any Manta tools) and so that these logs will not fill up their container.

Per RFD 0002, these will be the main source of "reliable" logs, as such we would also like to get them into Manta in a timely manner.

With Docker, because all the data is going through the docker daemon, what they do for each log line is basically:

• stat the log file
  • if the size is > max-size, rotate() and re-open
• write the new entry

The rotate() function here then checks the max-file and renames .8->.9, .7->.8, etc. and then renames the current log. This way when the write immediately following a file reaching max-size occurs, it'll be rotated immediately.

Proposal (no-Manta)

If Manta is not available most of the rest of this discussion does not apply. In that case, what we will do is use the same watcher agent as described below, but:

• when the size of the log is >= max-size:
  • move the log file to stdio.log.<YYYY><mm><dd>T<HH><MM><SS>Z
  • signal zoneadmd to re-open original log
  • if max-file is set, delete oldest until we're at count == max-file
  • nothing further

In this mode the zone will still fill up with logs unless the operator has setup some mechanism for archiving / deleting old log files.

Notes:

• max-size and max-file are only available when log-driver is json-file

Proposal (Manta)

We will write an agent that runs in the GZ, is installed with the other agents and:

• watches all docker container's stdio.log files (probably w/ event ports)
• when one of those files changes, do a stat and check against max-size
• if size >= max-size:
  • move log file to stdio.log.<YYYY><mm><dd>T<HH><MM><SS>Z
  • signal zoneadmd to re-open original log
  • leave hermes to deal with uploading and max-file
• when a container is deleted, upload the stdio.log file from the archive and delete it

We will modify vmadm to include the stdio.log file in the files that get archived when a VM is deleted. On deletion the stdio.log file should also be renamed to match the timestamp pattern of the other rotated files (and those in Manta).

We will modify hermes to support uploading to a customer's Manta area based on the owner_uuid of the container, and also to support a limited number of remote files. We will also make any other required modifications for hermes to pick up and upload these files.

This will mean that:

• docker logs will be the primary way to access recent logs for your container
• logs which have reached the maximum size or for containers which have been destroyed will be available in Manta

Notes:

• max-size and max-file are only available when log-driver is json-file

Things considered

Hermes

Josh Clulow points out:

[...] I think we should use hermes to achieve the upload/archival portion
of this.  It would probably require some modification to support the idea of
uploading to an account other than "admin", but the actual upload engine
already does basically everything that would be required:

- Manta configuration through SAPI
- upload parallelism
- retries on failure
- uploading through a DC-wide proxy
- converting local rotated log file names into Manta paths
  based on token expansion, mtime, etc
- debouncing mtime to ensure we don't upload a file that's
  still being written to
- deleting files only once successfully uploaded, potentially
  with a limited retention of already-uploaded files on the
  local system

The Manta proposal above relies on the use of hermes.

Support for max-file or max-size

There was some discussion on whether we should support these at all. If we were using a periodic scanner to do the uploading (e.g. something that ran every 5 minutes and always uploaded if there was data) max-size would never make any sense. With Manta, unlike a local disk, storage space is less of a concern so it's not clear in this model that max-file is necessary either.

Unlike Docker, we're logging to the GZ log with drivers other than json-file. If we want to allow --log-opt max-file=3 for all drivers, it may be confusing for users. Since all other options for the various log drivers are prefixed with the driver name such as syslog-address.

The most recent suggestion here is:

• support max-size and max-file, but only for the json-file driver
• for drivers other than json-file and when not specified, the max-size and max-file will have default values (actual values TBD)

Rotation Strategy

Given that we have a container and it has data written to:

/zones/<vm_uuid>/logs/stdio.json

a few questions arise:

• what should notice that a new docker container with a log showed up?
• what should rotate that file?
• how frequently should the rotation occur?
• should we skip empty logs?
• how do we find the manta login for the owner_uuid of the VM? Mahi?

One option would be to have a new agent that runs in the GZ of all nodes and periodically looks at /zones/*/logs/ for non-empty files, rotates them and then consumes the file while sending to Manta. Since this would be running in the GZ though, it would need to proxy through another zone (perhaps sdc zone) in order to talk to Manta. It would also need to find the owner_uuid's Manta login so that it knows the path to write the log.

Another option might be to have logadm rotate /zones/*/logs/stdio.log on some frequency and have another separate tool (or maybe hermes?) which takes the rotated files and uploads them. Since we would like to keep the latency between the logs being written to disk and showing up in Manta minimal, it seems like for this mode we might need to have logadm and hermes run more frequently, as currently both run hourly.

A new option was raised after the initial draft of this, which was to have a new agent but have it watch files and rotate when they hit max-size. This behavior is much closer to Docker's and would allow us to upload files much less frequently to Manta on average. As such, it's what we've chosen for the current proposal above.

Other considerations here (apply to the first two options):

• given that we can potentially have over 2000 containers per CN (assuming 128M containers and 256G CN) and we can have 1000 CNs per DC... How problematic is it to write up to 2M files to Manta every 5 minutes per DC? At what rate would we start having problems? Not writing empty files would likely help decrease this number significantly.
• if we're going to use logadm we may need to first fix OS-3097 and related tickets.

Manta Paths

Original thinking was that we could use the same directory the old KVM-based docker service used for logs in Manta. This was:

/<login>/stor/.joyent/docker/logs/<vm_uuid>

in our case we'd replace <vm_uuid> with <docker_id> since that's the id that customers would see with their docker clients. And under this directory what I would propose is that we have files named something like:

.../<YYYY>/<mm>/<dd>/<HH>/stdio.log.<YYYY><mm><dd>T<HH><MM><SS>Z

That's 4-digit year, 2-digit month, 2 digit day-of-month, 2 digit hour (00-23), and additionally in the filename, the 2 digit minute and 2 digit second. This would be the UTC timestamp of the time the file was rotated.

One suggestion that was made was that we ensure the filename of the rotated files in the GZ of the CNs matches the directory and filename of the files in Manta for easier comparison during uploads. This seems quite reasonable so I've updated the rotation to use this format too.

A suggestion has also been made that we make this configurable, potentially even configurable via cloudapi per-login using something like:

• https://mo.joyent.com/docs/cloudapi/master/#config

and/or a SAPI metadata variable. Either of these would obviously add additional complexity.

Container Deletion

When a container is deleted between the log-rotation periods, it's likely that data will still be in its stdio.log that has not yet been sent to Manta. In order to prevent losing logs here, I'd suggest that we change the archive_on_delete feature such that it knows to also keep the stdio.log files in the archived data and have the thing doing rotation also look here for the last logs to upload for a container.

Inspect Output

One suggestion was made that we query sdc-docker at the time of rotation and get the /containers/<docker_id>/json output and add that to the root directory for the container.

If we did this, we would need to do something differently for destroyed containers as they would not show up in sdc-docker.

We'd also need to figure out how to query sdc-docker as the owner of the container.

More Tools

With logs going into Manta, it has been suggested that people would want tools to manage these other than the m* tools. (mls, mget, mfind, etc.)

Knowing when all logs are uploaded

Trent suggested a use case of wanting to be able to script knowing when a final log upload was complete. Ignore the "container didn't log" case where there will be no uploaded log files. The use case could theoretically be handled if the last log upload used the same timestamp [or a later one] as a 'destroy' time in the cloudapi MachineAudit.

JoshW points out that some VMs will never have any logs uploaded (if nothing ever got written to stdout/stderr) which means users may be waiting for a log

= destroy time that will never show up.

Open Questions

• what should the defaults be for max-size and max-file?
  • for drivers other than json-file, we'll always only use these defaults
• what path should we use?
  • Original suggestion was /<login>/stor/.joyent/docker/logs/<docker_id>, but others have suggested we not use that
• do we want to include the inspect output with the container?
• can we leave cli tools out of scope?
• any other major concerns that were missed?

Tickets

• OS-4898 for archiving stdio.log when VM is destroyed
• AGENT-942 for agent that rotates logs
• AGENT-943 for having hermes know how to rotate these logs to Manta