Allow using a local infra_image

[varsanojidan]

Proposal

Allow specifying a local infra_image under docker config in order to avoid pulling the image.

Use-cases

For my current usecase, I would like to avoid having nomad reach out to pull images at all if possible, so I was hoping to use a local version of the infra image instead of Nomad pulling it.

I can see from the code that right now its always trying to pull the infra_image when setting up the network, and you cant specify a local image like you can for task images.

[shoenig]

Hi @varsanojidan, thanks for the suggestion! Indeed, looks like we don't do the same optimization around checking whether the infra_image is already downloaded like we do for task images, instead just always leaning on PullImage. I suspect most folks looking for this sort of behavior are actually running internal docker repositories, which get pulled from instead of the public docker hub. Being able to only use local images though would be a good improvement.

[l-monninger]

Are there any known sharp corners with this? I don't know what I did to my config, but I now can't pull gcr.io/google_containers/pause-amd64.

2022-09-17T09:55:11Z  Killing              Sent interrupt. Waiting 5s before force killing
2022-09-17T09:55:10Z  Setup Failure        failed to setup alloc: pre-run hook "network" failed: failed to create network for alloc: Failed to pull `gcr.io/google_containers/pause-amd64:3.1`: API error (500): Head "https://gcr.io/v2/google_containers/pause-amd64/manifests/3.1": unauthorized: Not Authorized.
2022-09-17T09:55:10Z  Sibling Task Failed  Task's sibling "connect-proxy-tl-rpc" failed
2022-09-17T09:54:03Z  Received             Task received by client

And, when I add the pull to my startup script, I successfully pull the image:

REPOSITORY                             TAG       IMAGE ID       CREATED         SIZE
<none>                                 <none>    0c946b4c9fa5   2 days ago      856MB
hello-world                            latest    feb5d9fea6a5   11 months ago   13.3kB
golang                                 1.15      40349a2425ef   13 months ago   840MB
gcr.io/google_containers/pause-amd64   3.1       da86e6ba6ca1   4 years ago     742kB

But, the error remains. Which would suggest to me that the local infra_image is not being used. Do I need to make sure it's not using latest?

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