69 lines
3.5 KiB
Markdown
69 lines
3.5 KiB
Markdown
---
|
|
stage: Enablement
|
|
group: Distribution
|
|
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
|
|
---
|
|
|
|
# Switching to Puma
|
|
|
|
As of GitLab 12.9, [Puma](https://github.com/puma/puma) has replaced [Unicorn](https://yhbt.net/unicorn/)
|
|
as the default web server. From GitLab 13.0, the following run Puma instead of Unicorn unless
|
|
explicitly configured not to:
|
|
|
|
- All-in-one package-based installations.
|
|
- Helm chart-based installations.
|
|
|
|
## Why switch to Puma?
|
|
|
|
Puma has a multi-thread architecture which uses less memory than a multi-process
|
|
application server like Unicorn. On GitLab.com, we saw a 40% reduction in memory
|
|
consumption.
|
|
|
|
Most Rails applications requests normally include a proportion of I/O wait time.
|
|
During I/O wait time MRI Ruby will release the GVL (Global VM Lock) to other threads.
|
|
Multi-threaded Puma can therefore still serve more requests than a single process.
|
|
|
|
## Configuring Puma to replace Unicorn
|
|
|
|
Beginning with GitLab 13.0, Puma is the default application server. We plan to remove support for
|
|
Unicorn in GitLab 14.0.
|
|
|
|
When switching to Puma, Unicorn server configuration
|
|
will _not_ carry over automatically, due to differences between the two application servers. For Omnibus-based
|
|
deployments, see [Configuring Puma Settings](https://docs.gitlab.com/omnibus/settings/puma.html#configuring-puma-settings).
|
|
For Helm based deployments, see the [Webservice Chart documentation](https://docs.gitlab.com/charts/charts/gitlab/webservice/index.html).
|
|
|
|
Additionally we strongly recommend that multi-node deployments [configure their load balancers to use the readiness check](../load_balancer.md#readiness-check) due to a difference between Unicorn and Puma in how they handle connections during a restart of the service.
|
|
|
|
## Performance caveat when using Puma with Rugged
|
|
|
|
For deployments where NFS is used to store Git repository, we allow GitLab to use
|
|
[direct Git access](../gitaly/index.md#direct-access-to-git-in-gitlab) to improve performance using
|
|
[Rugged](https://github.com/libgit2/rugged).
|
|
|
|
Rugged usage is automatically enabled if direct Git access
|
|
[is available](../gitaly/index.md#how-it-works)
|
|
and Puma is running single threaded, unless it is disabled by
|
|
[feature flags](../../development/gitaly.md#legacy-rugged-code).
|
|
|
|
MRI Ruby uses a GVL. This allows MRI Ruby to be multi-threaded, but running at
|
|
most on a single core. Since Rugged can use a thread for long periods of
|
|
time (due to intensive I/O operations of Git access), this can starve other threads
|
|
that might be processing requests. This is not a case for Unicorn or Puma running
|
|
in a single thread mode, as concurrently at most one request is being processed.
|
|
|
|
We are actively working on removing Rugged usage. Even though performance without Rugged
|
|
is acceptable today, in some cases it might be still beneficial to run with it.
|
|
|
|
Given the caveat of running Rugged with multi-threaded Puma, and acceptable
|
|
performance of Gitaly, we disable Rugged usage if Puma multi-threaded is
|
|
used (when Puma is configured to run with more than one thread).
|
|
|
|
This default behavior may not be the optimal configuration in some situations. If Rugged
|
|
plays an important role in your deployment, we suggest you benchmark to find the
|
|
optimal configuration:
|
|
|
|
- The safest option is to start with single-threaded Puma. When working with
|
|
Rugged, single-threaded Puma works the same as Unicorn.
|
|
- To force Rugged to be used with multi-threaded Puma, you can use
|
|
[feature flags](../../development/gitaly.md#legacy-rugged-code).
|