Modify "join_cluster" to key off of "known_servers". Fixes #31.

[tehranian]

The existing implementation of join_cluster relies upon num_peers, which doesn't exist anymore. Modify join_cluster to use known_servers instead.

I tested this with a set of 3 Vagrant boxes running puppet. Before join_cluster runs, I see:

$ consul info | grep known
  known_servers = 0

And after join_cluster runs I see:

$ consul info | grep known
known_servers = 1

$ consul members
Node               Address               Status  Type    Build  Protocol
vi-cobbler11       192.168.181.146:8301  alive   client  0.4.1  2
vi-devops-consul9  192.168.181.142:8301  alive   server  0.4.1  2
vi-cobbler10       192.168.181.129:8301  alive   client  0.4.1  2

[solarkennedy]

This this really the right thing?

Can't consul have known_servers even if it hasn't joined a cluster yet? (via serf gossip)

Deferring to @EvanKrall

[tehranian]

Hi there,

Yea, I was thinking about this after I sent the pull request... While I think this patch provides a solution that works in some cases, I don't think that it's the best possible solution.

Another idea:

• Whereas the "join_cluster" parameter is the hostname or IP of a single known consul node...
• Do a name resolution on the DNS hostname, and see if the resulting IP is in the output of consul members.
  • If the user provides an IP, no need to resolve
  • This would work in the situation where the DNS name is a CNAME instead of an A record, which I suspect could be a common use case.

Here's the sample output of consul members in my Vagrant test environment:

$ consul members
Node               Address               Status  Type    Build  Protocol
vi-devops-consul9  192.168.181.129:8301  alive   server  0.4.1  2
vi-cobbler11       192.168.181.146:8301  alive   client  0.4.1  2
vi-cobbler10       192.168.181.142:8301  alive   client  0.4.1  2

What do you think?

[EvanKrall]

The DNS/consul members thing seems reasonable.

The existing patch wouldn't converge on machines that are acting as the servers - for whatever reason, consul info doesn't have a known_servers line when you're on a server.

[tehranian]

Thanks @EvanKrall .

re: DNS/"consul members" - Hmmm now that I think about it, a conditional that converts a hostname to DNS or leaves an IP address as-is, then greps the output of "consul members" for it in a single line of bash is going ugly. Any ideas?

I'm thinking of something like the following which seems to convert hostnames to an IP, or leave the IP as-is.

getent ahostsv4 www.google.com | grep STREAM | head -n 1 | cut -d ' ' -f 1

Then that can be fed as the argument for "grep". Ex:

consul members | grep `getent ahostsv4 www.google.com | grep STREAM | head -n 1 | cut -d ' ' -f 1`

[solarkennedy]

join_cluster is now deprecated. This kind of output manipulation is a little much.
Maybe someone ambitious will just add something to consul's output like "cluster status: joined" to make it way easier to parse or something.

Till then I'm leaving this as an exercise to the implementer.