Add deployment strategies

[chrisbaldauf]

This adds 5 deployment strategies that can be set either via the command line or through Vagrantfile config. The strategies are fully documented in docs/strategy.md, but I can summarize:

• serial (default) - one at a time
• parallel - all at the same time
• canary - one, pause, the rest in parallel
• blue_green - half, pause, then the rest in parallel
• canary_blue_green - one, pause, half in parallel, pause, the rest in parallel

These can be passed on the command line with --strategy parallel or set in the Vagrantfile with config.orchestrate.strategy = :parallel.

Prompting can be surpressed via the command line with -f or --force or in the Vagrantfile with config.orchestrate.force_push = true

@maclennann @potashj

[potashj]

I like the prompt between groups. Makes the canary strategy useful. The "blue_green" however seems to be more of a half-canary than a true blue green. What I mean is, instead of the live set of machines (say blue) being replaced by the upgraded set (green), followed by the blue set being taken out of commission, you're just provisioning half and then the other. Not sure if the disconnect between the implementation and the implication is worthy of a rename, but just something to consider.

[maclennann]

I dig it. It would be nice if it gave more debug log information about what it was going to do or had just done (e.g. "deploying to next # machines" or "deploying to hosta,hostb,hostc")

[chrisbaldauf]

@maclennann +1 for more debugging information. I'll add it.

[chrisbaldauf]

...
DEBUG push: Finished orchestrating push to group number 1 of 2.
DEBUG push: Orchestrating push to group number 2 of 2.
DEBUG push:  -- Hosts: server2,server3,server4,server5,server6
...

[ryanbreen]

What does this message mean? What hosts are in group 1? server1?

[chrisbaldauf]

Yes, this is a snippet of the log from the middle (end of group 1 and start of group 2). The full output would be:

DEBUG push: Orchestrating push to group number 1 of 2.
DEBUG push:  -- Hosts: server1
...
DEBUG push: Finished orchestrating push to group number 1 of 2.
DEBUG push: Orchestrating push to group number 2 of 2.
DEBUG push:  -- Hosts: server2,server3,server4,server5,server6
...
DEBUG push: Finished orchestrating push to group number 2 of 2.

[ryanbreen]

Cool!