231 lines
8.4 KiB
ReStructuredText
231 lines
8.4 KiB
ReStructuredText
Tuning
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======
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This page contains a collection of tips and settings that can be used to
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tune your server based upon its users and the other servers it federates
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with.
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We recommend that all installations are run behind a CDN, and
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have caches configured. See below for more details on each.
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Scaling
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-------
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The only bottleneck, and single point of failure in a Takahē installation is
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its database; no permanent state is stored elsewhere.
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Provided your database is happy (and PostgreSQL does a very good job of just
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using more resources if you give them to it), you can:
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* Run more webserver containers to handle a higher request load (requests
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come from both users and other ActivityPub servers trying to forward you
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messages). Consider setting up the DEFAULT cache under high request load, too.
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* Run more Stator worker containers to handle a higher processing load (Stator
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handles pulling profiles, fanning out messages to followers, and processing
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stats, among others). You'll generally see Stator load climb roughly in
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relation to the sum of the number of followers each user in your instance has;
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a "celebrity" or other popular account will give Stator a lot of work as it
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has to send a copy of each of their posts to every follower, separately.
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As you scale up the number of containers, keep the PostgreSQL connection limit
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in mind; this is generally the first thing that will fail, as Stator workers in
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particular are quite connection-hungry (the parallel nature of their internal
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processing means they might be working on 50 different objects at once). It's
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generally a good idea to set it as high as your PostgreSQL server will take
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(consult PostgreSQL tuning guides for the effect changing that settting has
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on memory usage, specifically).
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If you end up having a large server that is running into database performance
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problems, please get in touch with us and discuss it; Takahē is young enough
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that we need data and insight from those installations to help optimise it more.
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Stator (Task Processing)
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------------------------
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Takahē's background task processing system is called Stator, and it uses
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asynchronous Python to pack loads of tasks at once time into a single process.
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By default, it will try to run up to 100 tasks at once, with a maximum of 40
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from any single model (FanOut will usually be the one it's doing most of).
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You can tweak these with the ``TAKAHE_STATOR_CONCURRENCY`` and
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``TAKAHE_STATOR_CONCURRENCY_PER_MODEL`` environment variables.
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The only real limits Stator can hit are CPU and memory usage; if you see your
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Stator (worker) containers not using anywhere near all of their CPU or memory,
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you can safely increase these numbers.
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Federation
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----------
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ActivityPub, as a federated protocol, involves talking to a lot of other
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servers. Sometimes, those servers may be under heavy load and not respond
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when Takahē tries to go and fetch user details, posts, or images.
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There is a ``TAKAHE_REMOTE_TIMEOUT`` setting to specify the number of seconds
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Takahē will wait when making remote requests to other Fediverse instances; it
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is set to 5 seconds by default. We recommend you keep this relatively low,
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unless for some reason your server is on a very slow internet link.
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This may also be a tuple of four floats to set the timeouts for
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connect, read, write, and pool timeouts::
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TAKAHE_REMOTE_TIMEOUT='[0.5, 1.0, 1.0, 0.5]'
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Note that if your server is unreachable (including being so slow that other
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servers' timeouts make the connection fail) for more than about a week, some
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servers may consider it permanently unreachable and stop sending posts.
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Caching
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-------
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There are two ways Takahē uses caches:
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* For caching rendered pages and responses, like user profile information.
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These caches reduce database load on your server and improve performance.
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* For proxying and caching remote user images and post images. These must be
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proxied to protect your users' privacy; also caching these reduces
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your server's consumed bandwidth and improves users' loading times.
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By default Takakē has Nginx inside its container image configured to perform
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read-through HTTP caching for the image and media files, and no cache
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configured for page rendering.
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Each cache can be adjusted to your needs; let's talk about both.
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Page Caching
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~~~~~~~~~~~~
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This caching helps Takahē avoid database hits by rendering complex pages or
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API endpoints only once, and turning it on will reduce your database load.
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There is no cache enabled for this by default
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To configure it, set the ``TAKAHE_CACHES_DEFAULT`` environment variable.
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We support anything that is available as part of
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`django-cache-url <https://github.com/epicserve/django-cache-url>`_, but
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some cache backends will require additional Python packages not installed
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by default with Takahē. More discussion on some major backends is below.
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Redis
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#####
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Examples::
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redis://redis:6379/0
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redis://user:password@redis:6379/0
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rediss://user:password@redis:6379/0
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A Redis-protocol server. Use ``redis://`` for unencrypted communication and
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``rediss://`` for TLS.
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Memcache
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########
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Examples::
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memcached://memcache:11211?key_prefix=takahe
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memcached://server1:11211,server2:11211
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A remote Memcache-protocol server (or set of servers).
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Filesystem
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##########
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Examples::
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file:///var/cache/takahe/
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A cache on the local disk. Slower than other options, and only really useful
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if you have no other choice.
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Note that if you are running Takahē in a cluster, this cache will not be shared
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across different machines. This is not quite as bad as it first seems; it just
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means you will have more potential uncached requests until all machines have
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a cached copy.
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Local Memory
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############
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Examples::
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locmem://default
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A local memory cache, inside the Python process. This will consume additional
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memory for the process, and should be used with care.
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Image and Media Caching
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~~~~~~~~~~~~~~~~~~~~~~~
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In order to protect your users' privacy and IP addresses, we can't just send
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them the remote URLs of user avatars and post images that aren't on your
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server; we instead need to proxy them through Takahē in order to obscure who
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is requesting them.
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Some other ActivityPub servers do this by downloading all media and images as
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soon as they see it, and storing it all locally with some sort of clean-up job;
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Takahē instead opts for using a read-through cache for this task, which uses
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a bit more bandwidth in the long run but which has much easier maintenance and
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better failure modes.
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Our Docker image comes with this cache built in, as without it you'll be making
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Python do a lot of file proxying on every page load (and it's not the best at
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that). It's set to 1GB of disk on each container by default, but you can adjust
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this by setting the ``TAKAHE_NGINX_CACHE_SIZE`` environment variable to a value
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Nginx understands, like ``10g``.
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The cache directory is ``/cache/``, and you can mount a different disk into
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this path if you'd like to give it faster or more ephemeral storage.
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If you have an external CDN or cache, you can also opt to add your own caching
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to these URLs; they all begin with ``/proxy/``, and have appropriate
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``Cache-Control`` headers set.
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CDNs
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----
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Takahē can be run behind a CDN if you want to offset some of the load from the
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webserver containers. Takahē has to proxy all remote user avatars and images in
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order to protect the privacy of your users, and has a built-in cache to help
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with this (see "Caching" above), but at large scale this might start to get
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strained.
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If you do run behind a CDN, ensure that your CDN is set to respect
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``Cache-Control`` headers from the origin rather than going purely off of file
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extensions. Some CDNs go purely off of file
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extensions by default, which will not capture all of the proxy views Takahē
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uses to show remote images without leaking user information.
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If you don't want to use a CDN but still want a performance improvement, a
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read-through cache that respects ``Cache-Control``, like Varnish, will
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also help if placed in front of Takahē.
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Sentry.io integration
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---------------------
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Takahē can optionally integrate with https://sentry.io for collection of raised
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exceptions from the webserver or Stator.
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To enable this, set the ``TAKAHE_SENTRY_DSN`` environment variable to the value
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found in your sentry project:
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``https://<org>.sentry.io/settings/projects/<project>/keys/``
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Other Sentry configuration can be controlled through environment variables
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found in ``takahe/settings.py``. See the
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`Sentry python documentation <https://docs.sentry.io/platforms/python/configuration/options/>`_
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for details.
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