[docker service update] - allow updates to a new version of the image, by tag

[sixeyed]

This is a feature request. Currently you can only update services with --image. You can replace a service with another image altogether, but there's potential for error when you only want to update to a new tag from the same image repo.

In a workflow where your release version is in the tag, you wouldn't normally update by anything other than the tag. docker service update --tag v1.2.3 (or similar) would support that, removing the risk of updating one service with the image for a different service.

[glyif]

dibs

[thaJeztah]

@glyif be aware that this is a proposal, and was not yet decided on, so design has to be reviewed still.

e.g., Things I can think of is;

• what if both --image foo:bar and --tag baz were provided
• is this opening the road to many more similar requests (e.g. update just a port for a --publish without affecting other options

[glyif]

@thaJeztah, thanks for the heads up. I'll hold off on this then until a decision has been made :)

[thaJeztah]

ping @dnephin @vdemeester @aaronlehmann any thoughts?

[aaronlehmann]

I don't feel strongly for or against adding a --tag flag. All the normal concerns apply about having two flags that are similar but have different semantics. But I can see that a --tag flag would be convenient in some cases.

[glyif]

maybe we can use a different flag other than --tag? thoughts?

[dnephin]

I don't like the idea of having two flags that do basically the same thing.

[glyif]

@dnephin @thaJeztah @aaronlehmann what are good next steps? should this be implemented?

[glyif]

Just checking up on this, have some time this weekend to work on it if you peeps are ok with it 🍡

[sixeyed]

@dnephin - just following up here. The idea is that they don't do the same thing. --image lets you update the service to any image, --tag (or whatever) would force you to use the same image repo, but update to a different tag. I think it fits nicely with immutable repos.

[thaJeztah]

It looks like there's no real consensus on this one. I'm closing this ticket for now, but we may change our mind in future 😅