= Docker Logging and Monitoring =

<<TableOfContents>>

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== Utilities ==

The `docker(1)` utility offers some logging and monitoring functionality.

To view the usage statistics for all containers, try:

{{{
$ docker stats redis1 redis2

CONTAINER           CPU %               MEM USAGE / LIMIT     MEM %               NET I/O             BLOCK I/O
redis1              0.07%               796 KB / 64 MB        1.21%               788 B / 648 B       3.568 MB / 512 KB
redis2              0.07%               2.746 MB / 64 MB      4.29%               1.266 KB / 648 B    12.4 MB / 0 B
}}}

To print the log messages from a container in a manner similar to `tail --follow`, try:

{{{
docker logs --tail --follow redis1
}}}

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== Logging to Files ==

The default behavior is for `dockerd(8)` to write JSON-formatted messages to a distinct file for each container.

Especially for long-running containers, this can lead to log files that are too large to store or reasonably use. See [[Docker/Configuration#Logging|here]] for configuration options that will mitigate this.

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== Prometheus ==



=== Networking ===

For '''Prometheus''' monitoring, `dockerd(8)` will need to bind to an address and port.

If you aren't concerned with hardening your server, just use `0.0.0.0` and everything will work.

If all monitoring will be done locally, you can check the output of `ip addr show docker0` to find the exact intranet address that `dockerd(8)` has bound to.

When monitoring remote servers, the Prometheus client must connect to the same address that `dockerd(8)` is bound to. It is ''not possible'' to configure DNS for the client and bind to `127.0.0.1` on the server. The only workaround is for `dockerd(8)` to bind to `0.0.0.0`.



=== Docker Swarm ===

Docker must be running in [[Docker/Swarm|swarm mode]].

Configure `dockerd(8)` to advertise metrics. This is an experimental feature, so the `dockerd(8)` configuration file must be updated like:

{{{
{
  "metrics-addr": "0.0.0.0:9323",
  "experimental": true
}
}}}



=== Prometheus Service ===

Prometheus needs to be configured to scrape `dockerd(8)` and publish it's database.

{{{
global:
  scrape_interval:     15s # Default is 60s
  evaluation_interval: 15s # Default is 60s
  # scrape_timeout default is 10s
  external_labels:
    monitor: 'my-monitor'

scrape_configs:
  - job_name: 'prometheus'
    static_configs:
      - targets: ['127.0.0.1:9090']

  - job_name: 'docker'
    static_configs:
      - targets: ['172.17.0.1:9323', 'example.com:9323']
}}}

Start one instance of Prometheus to the swarm.

{{{
docker service create --replicas=1 --name prometheus \
    --mount type=bind,src=/path/to/prometheus.yml,dst=/etc/prometheus/prometheus.yml \
    --publish 9090:9090/tcp \
    prom/prometheus
}}}

Verify that Prometheus has successfully connected to `dockerd(8)` at `http://127.0.0.1:9090/targets`.



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CategoryRicottone