Re: Master hooks needed

[Eric Wong <e@80x24.org>]

Bráulio Bhavamitra <braulio@eita.org.br> wrote:
> Hello all,
> 
> If I need to hook something after master load, I'm currently doing:
> 
> before_fork do |server, worker|
>   # worker 0 is the first to init, so hold the master here
>   if worker.nr == 0
>      #warm up server...
> 
>      #kill old pid...
>   end
> 
>   # other stuff for each worker
> end
> 
> Both operations I currently do (server warm up and old pid kill) need
> to be run only once, and not for every worker as before_fork does,
> that's why I had to put the condition seen above.

The above is fine if your first worker never dies.  I think you can add
a local variable to ensure it only runs the first time worker.nr == 0 is
started, in case a worker dies.  Something like:

    first = true
    before_fork do |server, worker|
      # worker 0 is the first to init, so hold the master here
      if worker.nr == 0 && first
         first = false
         #warm up server...

         #kill old pid...
      end

      # other stuff for each worker
    end

For what it's worth, I'm not a fan of auto-killing the old PID in the
unicorn config and regret having it in the example config.  It's only
for the most memory-constrained configs and fragile (because anything
with pid files is always fragile).

> So hooks for master is needed, something like
> master_after_load(server) and master_init(server).
> 
> What do you think?

rack.git also has a Rack::Builder#warmup method.  Aman originally
proposed it for unicorn, but it's useful outside of unicorn so
we moved it to Rack.

In general, I'm against adding new hooks/options because they tend to
make maintainability and documentation harder for ops folks.
I still have nightmares of some Capistrano config filled with hooks
from years ago :x

Features like these also makes migrating away from unicorn harder, so
that is another reason we ended up adding #warmup to Rack and not
unicorn.