[proxy] Add IPAM support

[paulbellamy]

No description provided.

[rade]

strawman:

1. make -e WEAVE_CIDR= (i.e. an empty WEAVE_CIDR) perform IPAM
2. add a --ipam flag to the proxy startup, which enables a mode in which all container starts without a WEAVE_CIDR will do IPAM

[paulbellamy]

@rade:
For 1, could make -e WEAVE_CIDR=auto perform IPAM, as blank var vs unset var could be confusing to users. (And giving special semantics to a blank CIDR feels kludgey)

For 2, any reason not to make this the default? It is the default for the router, correct?

[paulbellamy]

Also for 2, is there a way for the proxy to ask the router if IPAM is enabled? Adds a bit of complexity around what to do if the router is unavailable, but we need to handle that anyway.

[rade]

The reason to go for blank vars is consistency with how IPAM gets triggered in weave commands. i.e. IPAM is used iff the user did not supply any IPs. I don't mind supporting =auto too.

I don't think automatic IPAM should be the default; just like --with-dns shouldn't be. Our proxy should be a null-op proxy unless the user does something special, i.e. adorn their containers with WEAVE_CIDRs or supply some flags on proxy launch.

I'd leave out the 'figure out whether IPAM is enabled'. Can do that later if we feel like it.

[paulbellamy]

Personally, I'd expect docker run -e 'WEAVE_CIDR=' ubuntu to have the same behaviour as docker run ubuntu. Which makes me favour option 2, with an eye to deprecating --ipam for auto-detection in the future.

[bboreham]

is there a way for the proxy to ask the router if IPAM is enabled?

The /status http request will have a line beginning 'Allocator'. I don't think there is any more direct route, but one could easily be added.

[rade]

I'd expect docker run -e 'WEAVE_CIDR=' ubuntu to have the same behaviour as docker run ubuntu.

I would not!

with an eye to deprecating --ipam for auto-detection in the future.

Then you are left with no way of using the proxy for ordinary (non-weave) containers.

[paulbellamy]

Since being able to use the proxy for both weave and non-weave containers is quite important, then option 1 is probably a better choice.

So, let's make WEAVE_CIDR= enable IPAM for that container. With no support for "...=auto", as it adds one more thing for users to learn with no benefit.