Background

We use File as a reliable and simple storage for logs, Running docker containers stores logs in files with container id file name which is hard to locate because are stored in:

/var/lib/docker/containers/<container id>/<container id>-json.log

Features

• Send containers stdout/stderr to a File.

• Integrates seamlessly with orchestration platforms like Kubernetes, Mesos/Marathon or Docker Swarm

• Output format of logs (dictionary)

  • Level of log at docker container (level)
  • JSON messages with all important container meta data (msg)
    • Container ID (container_id)
    • Container name (container_name)
    • Container creation date (container_created)
    • Image ID (image_id)
    • Image name (image_name)
    • Command including ENTRYPOINT and arguments (command)
    • Log tag as provided via --log-tag option (tag)
    • Extra information as defined via --log-opt labels= or --log-opt env= (extra)
    • Host that container runs on (host)
    • Timestamp when log was generated (timestamp)
    • Raw log line produced by child process (message)
  • Time of log in docker contrainer (time)

• message payload may be arbitrarily complex (e.g. JSON encoded)

• You can also configure logging setup either globally through Docker config.json or per container (--log-opt style)

Requirements

• Docker >= 17.05 (since that brings log driver plugin support).
• How to install
• Check docker version

  $ sudo docker version
  Client:
  Version:	17.12.0-ce
  API version:	1.35
  Go version:	go1.9.2
  Git commit:	c97c6d6
  Built:	Wed Dec 27 20:11:19 2017
  OS/Arch:	linux/amd64
  
  Server:
  Engine:
  Version:	17.12.0-ce
  API version:	1.35 (minimum version 1.12)
  Go version:	go1.9.2
  Git commit:	c97c6d6
  Built:	Wed Dec 27 20:09:53 2017
  OS/Arch:	linux/amd64
  Experimental:	false
  

• Docker for Windows isn't supported at the moment (see https://docs.docker.com/engine/extend/)

Install

cd docker-file-log-driver
bash runs.sh

Check

$ docker plugin ls
ID                  NAME                     DESCRIPTION         ENABLED
8c7587db6fdc        file-log-driver:latest   File log driver     true

Usage

Basic usage

Run a container using this plugin:

$ docker run --log-driver file-log-driver --log-opt fpath=/testing/test.log alpine date
Tue Feb 27 06:13:36 UTC 2018

Note: log file --log-opt fpath is stored inside /var/log/fpath i.e. fpath=/testing/test.log originally is stored in /var/log/testing/test.log

Observe the logs inside path /var/log/fpath

$ sudo cat /var/log/testing/test.log |jq -r '.msg'| jq -r '.'
{
  "message": "Tue Feb 27 06:13:36 UTC 2018",
  "container_id": "dd3662cd039c3ffb39cdddfe16bf8ca4ee7eeae25080df20f51b1bdf7d6b2f1a",
  "container_name": "blissful_varahamihira",
  "container_created": "2018-02-27T06:13:35.445157368Z",
  "image_id": "sha256:3fd9065eaf02feaf94d68376da52541925650b81698c53c6824d92ff63f98353",
  ...
}

Advanced usage

This example shows the usage of

• Custom log tags (c.f. https://docs.docker.com/engine/admin/logging/log_tags/)
• Container label logging
• Container environment variable logging

$ docker run --label foo=abc --label bar=xyz -e SOME_ENV_VAR=foobar --log-driver file-log-driver --log-opt fpath=/testing/test2.log --log-opt "tag={{.ImageName}}/{{.Name}}/{{.ID}}" --log-opt labels=foo,bar --log-opt env=SOME_ENV_VAR alpine date
Tue Feb 27 07:20:32 UTC 2018

Observe the logs inside path /var/log/fpath

$ sudo cat /var/log/testing/test2.log |jq -r '.msg'| jq -r '.'
{
  "message": "Tue Feb 27 07:20:32 UTC 2018",
  "container_id": "3332274db729219ed738458eb120ddc64436513199d182fa7a9fe635363983ce",
  "container_name": "serene_leavitt",
  "container_created": "2018-02-27T07:20:31.729281471Z",
  "image_id": "sha256:3fd9065eaf02feaf94d68376da52541925650b81698c53c6824d92ff63f98353",
  ...
}

Options

All available options are documented here and can be set via --log-opt KEY=VALUE. Timeouts need to be specified in a format supported by https://golang.org/pkg/time/#ParseDuration.

Key	Default	Description
fpath	/var/log/docker/docker_file_log_driver_default.log	File path of the log file inside /var/log
max-size	10	size in mb of each log file
max-backups	10	number of log file backups after max-size is reched
max-age	100	number of days log files are kept in the file system before dleting

Uninstall

To uninstall, please make sure that no containers are still using this plugin. After that, disable and remove the plugin like this:

$ docker plugin disable file-log-driver
$ docker plugin rm file-log-driver

Hack it

You're more than welcome to hack on this.:-)

$ git clone https://github.com/DoManhQuang/docker-file-log-driver
$ cd docker-file-log-driver
$ docker build -t docker-file-log-driver .
$ ID=$(docker create docker-file-log-driver true)
$ mkdir rootfs
$ docker export $ID | tar -x -C rootfs/
$ docker plugin create file-log-driver .
$ docker plugin enable file-log-driver