Docker Stats On Exit Shim

This is a small utility designed to capture the statistics for the run of a Docker container before its destruction.

It is designed to be used as the main process of a Docker container that wraps the real command by waiting for it to exit and then querying the active Cgroup subsystems to gather their statistics. It dumps these statistics to a file as JSON and then exits with the exit code of the real command.

Example

$ docker run --rm -ti -v`pwd`:/tmp/:rw ubuntu /tmp/docker-stats-on-exit-shim /tmp/output.json /bin/sleep 1
$ cat output.json

{
  "wall_time": 1000765975,
  "user_cpu_time": 0,
  "sys_cpu_time": 0,
  "cgroups": {
    "cpu_stats": {
      "cpu_usage": {
        "total_usage": 21326399,
        "percpu_usage": [
          14721062,
          1512284,
          1730836,
          3362217,
          0,
          0,
          0,
          0
        ],
        "usage_in_kernelmode": 0,
        "usage_in_usermode": 10000000
      },
      "throttling_data": {}
    },
    "memory_stats": {
    ...
    }
  }
}

Building

docker run --rm -ti -u $ID:$(id -g) -v $HOME/tmp:/home/ops/tmp hysds/dev bash --login
cd tmp
wget https://dl.google.com/go/go1.13.4.linux-amd64.tar.gz
sudo tar -C /usr/local -xzf go1.13.4.linux-amd64.tar.gz 
export PATH=$PATH:/usr/local/go/bin
mkdir -p src/github.com/hysds
export GOPATH=`pwd`
cd src/github.com/hysds
git clone https://github.com/hysds/docker-stats-on-exit-shim.git
cd docker-stats-on-exit-shim
git submodule init && git submodule update
go get .
go build

Caveats

• The recorded statistics won't quite be before container destruction but it's probably close enough.
• The recorded statistics will contain the run of the tool (i.e. it will contribute to CPU usage). It should be a very small contribution though.