How to know when a new docker container is created

Issue

What is the most optimal way for a process on a Linux PC to get informed automatically when a new Docker container is created ?

I know it is possible to check the date with Docker Engine API, but there is maybe a better solution, with file watchers or something like that ?

Solution

$ docker events --filter "type=container" --filter "event=create" --format "{{json .}}" | jq -r

will listen all docker events in real time and print only container create events like:

{
  "status": "create",
  "id": "0d4f9f...f072c1e305",
  "from": "hello-world",
  "Type": "container",
  "Action": "create",
  "Actor": {
    "ID": "0d4f9f9b8b20...7f072c1e305",
    "Attributes": {
      "desktop.docker.io/wsl-distro": "Debian",
      "image": "hello-world",
      "name": "lucid_engelbart"
    }
  },
  "scope": "local",
  "time": 1667446412,
  "timeNano": 1667446412029074700
}

Also, you may set dates:

$ docker events --since $(date "+%s" -d "-1 day") --until $(date "+%s") --filter "type=container" --filter "event=create" --format "{{json .}}" | jq -r

will print all events for one day.

Manual

Also, it is possible to use curl to get info via REST API:

$ curl -H "Content-Type: application/json" --unix-socket /var/run/docker.sock "http://localhost/events?since=$(date "+%s" -d "-1 day")&until=$(date "+%s")&filters=%7B%22event%22%3A%7B%22create%22%3Atrue%7D%2C%22type%22%3A%7B%22container%22%3Atrue%7D%7D" | jq

Docker is listening to Unix socket by default so --unix-socket parameter is needed. However, it is possible to connect to Docker via TCP socket, but you have to change Docker Engine parameters (Not sure but probably web socket may be used in this case?).
Also, if you set until parameter (CLI and curl the same) Docker will print all events until date and exit without continuous listening for new ones.

Of course, Docker libraries and SDKs may be used to get same output programmatically, but it depends on programming language, so it is hard to provide exact example

´╝Őpipelined jq is not necessary in real usage. I just added it for pretty printing.

PS. Thanks to @David Maze for the comment. Didn’t know about this feature before

Answered By – rzlvmp

This Answer collected from stackoverflow, is licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0

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