mirror of
https://github.com/puma/puma.git
synced 2022-11-09 13:48:40 -05:00
95 lines
4 KiB
Markdown
95 lines
4 KiB
Markdown
# Deployment engineering for puma
|
|
|
|
Puma is software that is expected to be run in a deployed environment eventually.
|
|
You can certainly use it as your dev server only, but most people look to use
|
|
it in their production deployments as well.
|
|
|
|
To that end, this is meant to serve as a foundation of wisdom how to do that
|
|
in a way that increases happiness and decreases downtime.
|
|
|
|
## Specifying puma
|
|
|
|
Most people want to do this by putting `gem "puma"` into their Gemfile, so we'll
|
|
go ahead and assume that. Go add it now... we'll wait.
|
|
|
|
|
|
Welcome back!
|
|
|
|
## Single vs Cluster mode
|
|
|
|
Puma was originally conceived as a thread-only webserver, but grew the ability to
|
|
also use processes in version 2.
|
|
|
|
Here are some rules of thumb:
|
|
|
|
### MRI
|
|
|
|
* Use cluster mode and set the number of workers to 1.5x the number of cpu cores
|
|
in the machine, minimum 2.
|
|
* Set the number of threads to desired concurrent requests / number of workers.
|
|
Puma defaults to 16 and that's a decent number.
|
|
|
|
#### Migrating from Unicorn
|
|
|
|
* If you're migrating from unicorn though, here are some settings to start with:
|
|
* Set workers to half the number of unicorn workers you're using
|
|
* Set threads to 2
|
|
* Enjoy 50% memory savings
|
|
* As you grow more confident in the thread safety of your app, you can tune the
|
|
workers down and the threads up.
|
|
|
|
#### Ubuntu / Systemd (Systemctl) Installation
|
|
|
|
See [systemd.md](systemd.md)
|
|
|
|
#### Worker utilization
|
|
|
|
**How do you know if you're got enough (or too many workers)?**
|
|
|
|
A good question. Due to MRI's GIL, only one thread can be executing Ruby code at a time.
|
|
But since so many apps are waiting on IO from DBs, etc., they can utilize threads
|
|
to make better use of the process.
|
|
|
|
The rule of thumb is you never want processes that are pegged all the time. This
|
|
means that there is more work to do that the process can get through. On the other
|
|
hand, if you have processes that sit around doing nothing, then they're just eating
|
|
up resources.
|
|
|
|
Watching your CPU utilization over time and aim for about 70% on average. This means
|
|
you've got capacity still but aren't starving threads.
|
|
|
|
## Daemonizing
|
|
|
|
I prefer to not daemonize my servers and use something like `runit` or `upstart` to
|
|
monitor them as child processes. This gives them fast response to crashes and
|
|
makes it easy to figure out what is going on. Additionally, unlike `unicorn`,
|
|
puma does not require daemonization to do zero-downtime restarts.
|
|
|
|
I see people using daemonization because they start puma directly via capistrano
|
|
task and thus want it to live on past the `cap deploy`. To this people I said:
|
|
You need to be using a process monitor. Nothing is making sure puma stays up in
|
|
this scenario! You're just waiting for something weird to happen, puma to die,
|
|
and to get paged at 3am. Do yourself a favor, at least the process monitoring
|
|
your OS comes with, be it `sysvinit`, `upstart`, or `systemd`. Or branch out
|
|
and use `runit` or hell, even `monit`.
|
|
|
|
## Restarting
|
|
|
|
You probably will want to deploy some new code at some point, and you'd like
|
|
puma to start running that new code. Minimizing the amount of time the server
|
|
is unavailable would be nice as well. Here's how to do it:
|
|
|
|
1. Don't use `preload!`. This dirties the master process and means it will have
|
|
to shutdown all the workers and re-exec itself to get your new code. It is not compatible with phased-restart and `prune_bundler` as well.
|
|
|
|
1. Use `prune_bundler`. This makes it so that the cluster master will detach itself
|
|
from a Bundler context on start. This allows the cluster workers to load your app
|
|
and start a brand new Bundler context within the worker only. This means your
|
|
master remains pristine and can live on between new releases of your code.
|
|
|
|
1. Use phased-restart (`SIGUSR1` or `pumactl phased-restart`). This tells the master
|
|
to kill off one worker at a time and restart them in your new code. This minimizes
|
|
downtime and staggers the restart nicely. **WARNING** This means that both your
|
|
old code and your new code will be running concurrently. Most deployment solutions
|
|
already cause that, but it's worth warning you about it again. Be careful with your
|
|
migrations, etc!
|