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I run a specific docker image for the first time:

docker run [OPTIONS] image [CMD]

Some of the options I supply include --link (link with other containers) and -p (expose ports)

I noticed that if I kill that container and simply do docker start <container-id>, Docker honors all the options that I specified during the run command including the links and ports.

Is this behavior explicitly documented and can I always count on the start command to reincarnate the container with all the options I supplied in the run command?

Also, I noticed that killing/starting a container which is linked to another container updates the upstream container's /etc/hosts file automatically:

A--(link)-->B (A has an entry in /etc/hosts for B)

If I kill B, B will normally get a new IP address. I notice that when i start B, the entry for B in A's /etc/hosts file is automatically updated... This is very nice.

I read here that --link does not handle container restarts... Has this been updated recently? If not, why am I seeing this behavior?

(Im using Docker version 1.7.1, build 786b29d)

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Forhad Ahmed
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  • That question was answered a year ago, it have probably changed. Look at github issues and pull requests – luxas Aug 06 '15 at 07:49

1 Answers1

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Yes, things work as you describe :)

You can rely on the behaviour of docker start as it doesn't really "reincarnate" your container; it was always there on disk, just in a stopped state. It will also retain any changes to files, but changes in RAM, such as process state, will be lost. (Note that kill doesn't remove a container, it just stops it with a SIGKILL rather than a SIGTERM, use docker rm to truly remove a container).

Links are now updated when a container changes IP address due to a restart. This didn't use to be the case. However, that's not what the linked question is about - they are discussing whether you can replace a container with a new container of the same name and have links still work. This isn't possible, but that scenario will be covered by the new networking functionality and "service" objects which is currently in the Docker experimental channel.

Adrian Mouat
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  • Thanks.. As a quick followup, do you know if there is any way for the docker host's `/etc/hosts` file to be modified to include all the containers' IP addresses with their names? So far, I haven't seen this anywhere but it would be very helpful. e.g: I have a container named `web` and another named `db`. I should be able to `ping web` and `ping db` from the host. – Forhad Ahmed Aug 07 '15 at 05:03
  • No, you need to use links to do that currently. Again, the new networking stuff in experimental will be of help here. – Adrian Mouat Aug 07 '15 at 07:26
  • Also, see stuff like registrator http://gliderlabs.com/registrator/latest/user/quickstart/ – Adrian Mouat Aug 07 '15 at 07:27