[chef] Re: Serial deployment

[Seth Falcon < >]

Hi Rob,

On Tue, Nov 2, 2010 at 10:38 AM, Rob Guttman 
<
 >
 wrote:
> We're just starting to use chef for managing nagios configs - so far, so
> good.

Nice :-)

> What we would like to eventually use it for is to deploy all of our web apps
> and services.  A specific use case we have is to be able to *serially*
> deploy to hosts/instances within a cluster behind a load balancer.  For
> example, we would take one host out of rotation, deploy to it, warm it up
> and/or smoke test, and when warming completes and/or if smoke tests pass
> then put it back into rotation and move on to the next host in the cluster.
>
> How best to achieve that?

Right now there isn't any automated tooling to support this sort of
deployment orchestration, but chef makes this fairly easy to manage in
a by-hand fashion.

Suppose you had a role for your app.  A first pass at serial deploy
would be:

0. Update data bag or role describing what version should be deployed.
1. Login to load balancer, take server 1 out of config, restart
2. Run chef-client on server 1.  Test it.  Put it in rotation and take
   out server 2.
[now repeat for each remaining server]


You could go a bit further by having the recipe that generates the
load balancer config check for an "active" attribute:

   web_apps = search(:node, "role:myapp AND active_app:true")

Then you could take a node out of rotation by editing the node with
knife, setting active_app:false, and running chef-client on the
load-balancer.  You could also use this attribute to decide where to
deploy next:

  knife ssh 'role:myall AND active_app:false' sudo chef-client

If you decide to experiment with this approach, you should be aware
that there is some lag (about 1 minute on the Opscode Platform)
between saving a node and being able to search for updated attribute
values.

+ seth