192 lines
6.9 KiB
ReStructuredText
192 lines
6.9 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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CDNs
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----
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Takahē is *designed to be run behind a CDN*. It serves most static files directly
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from its main webservers, which is inefficient if called directly, but they
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have ``Cache-Control`` headers set so that the CDN can do the heavy lifting -
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more efficiently than offloading all files to something like S3.
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If you don't run behind a CDN, things will still work, but even a medium
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level of traffic might put the webservers under a lot of load.
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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. 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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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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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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By default Takakē has caching disabled. The caching needs of a server can
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varying drastically based upon the number of users and how interconnected
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they are with other servers.
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There are multiple 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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The exact caches you can configure are:
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* ``TAKAHE_CACHES_DEFAULT``: Rendered page and response caching
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* ``TAKAHE_CACHES_MEDIA``: Remote post images and user profile header pictures
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* ``TAKAHE_CACHES_AVATARS``: Remote user avatars ("icons") only
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We recommend you set up ``TAKAHE_CACHES_MEDIA`` and ``TAKAHE_CACHES_AVATARS``
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at a bare minimum - proxying these all the time without caching will eat into
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your server's bandwidth.
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All caches are configured the same way - with a custom cache URI/URL. We
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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 backend is below.
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All items in the cache come with an expiry set - usually one week - but you
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can also configure a maximum cache size on dedicated cache datastores like
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Memcache. The key names used by the caches do not overlap, so there is
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no need to configure different key prefixes for each of Takahē's caches.
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Backends
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~~~~~~~~
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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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Redis has a large item size limit and is suitable for all caches. We recommend
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that you keep the DEFAULT cache separate from the MEDIA and AVATARS caches, and
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set the ``maxmemory`` on both to appropriate values (the proxying caches will
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need more memory than the DEFAULT cache).
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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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Memcached has a 1MB limit per key by default, so this is only suitable for the
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DEFAULT cache and not the AVATARS or MEDIA cache.
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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.
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This *will* work with any of the cache backends, but is probably more suitable
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for MEDIA and AVATARS.
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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 not be used with the MEDIA or AVATARS caches.
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