Etcd remote state backend

[edef1c]

I'd like to get this merged, it's incredibly useful for people already running CoreOS clusters
who still require some form of self-hosted infrastructure management.

The etcd project unfortunately doesn't provide a public demo server,
so the tests for this backend require providing an etcd endpoint.

[edef1c]

It should probably be noted that I'm base64-encoding the state, since etcd doesn't currently support binary values.

[edef1c]

I'm not sure if it's actually necessary to encode the values, given that they appear to be just JSON in practice.
The interface allows for arbitrary byte strings, however.

[apparentlymart]

I initially made the S3 backend use a generic MIME type because the interface allows arbitrary bytes, but we recently changed it to application/json because practically that is what it is.

Assuming you're going to get a valid JSON payload seems reasonable to me, and thus assuming that it will be UTF-8 encoded text.

[edef1c]

Okay, updated it to just deal with strings — I'm in favour of keeping things simple [=

[apparentlymart]

This looks great to me. Thanks!

Would you mind adding a section to the remote config docs describing how to use this? You could just use one of the others as an example. I think once there are docs here this will be good to go!

[apparentlymart]

Reading these docs made me spot something I didn't catch the first time around, because I tested with only one endpoint: isn't endpoints a list of URLs? It seems strange to me to delimit a list of URLs with commas because commas are valid within URLs.

I suppose practically-speaking an etcd endpoint URL is only going to contain a scheme, host and port and so there aren't any opportunities for commas there, but could it instead be a space-separated list of URLs so that e.g. auto-linkification algorithms used on various web forums won't be tempted to consider the whole list of endpoints to be a single, long URL?

For example, Github seems to exhibit the behavior I'm talking about:

-config="endpoints=http://127.0.0.1:1234/,http://127.0.0.1:4321/"

Not a huge deal, but something I could see being confusing to people trying to discuss Terraform.

[edef1c]

I considered spaces, I went for commas mainly because handling arguments with spaces in them in shell scripts is something people tend to mess up. Commas seemed rare enough in URLs for this to be worth it. I'm going to change this to spaces, though — two votes for spaces, and only one for commas.

[apparentlymart]

Sorry @nathan7 one more quick thing I didn't catch the first time. I know it's a bit of trivia but these things can be hard to change later so I'm interested to hear what you think.

[apparentlymart]

Awesome, thanks! Sorry for the messing around. 🚢

[apparentlymart]

When I merged this there was a build failure relating to packngo which seems to be in the packet provider and not related to this change. If I'm wrong please let me know and I'll clean it up.

[ghost]

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