Tuning

Rauthys default tuning is optimized for somewhat low resource usage while still providing good performance and low latency up to a couple of thousands of users. If you run a tiny instance with less than 100 users, or a very big one with users going into millions, or you need a very high degree of concurrency, you can optimize the default tuning. We will go through a few options to achieve what you need, no matter if you want even lower memory usage or higher throughput.

Database

cache_storage_disk

By default, Rauthy keeps the WAL + Snapshots for the in-memory cache on disk. This makes the cache, even though it exists in-memory only, persistent, because it can be rebuilt from disk after a restart. Blacklisted IPs for instance exists in the cache only, as well as Auth Codes and some other values. The other advantage is, that it reduces the overall memory usage a bit, because we don't need duplicate data in-memory just to make the Raft replication work.

These advantages are really nice and usually, because the throughput is really high anyway, you should not need to worry about it. However, you can optionally keep everything cache related in memory only. This boosts the throughput a lot, depending on the IOPS of your disk of course, at the cost of higher memory usage and the fact, that nodes need to re-join the Raft cluster after a restart and do a complete re-sync for latest Snapshot + Raft Logs.

To keep everything in memory only, set:

[cluster]
# Set to `false` to store Cache WAL files + Snapshots in-memory only.
# If you run a Cluster, a Node can re-sync cache data after a restart.
# However, if you restart too quickly or shut down the whole cluster,
# all your cached data will be gone.
# In-memory only greatly increases the throughput, though, so it
# depends on your needs, what you should prefer.
#
# default: true
# overwritten by: HQL_CACHE_STORAGE_DISK
cache_storage_disk = false

read_pool_size / pg_max_conn

These values define the database connection pool sizes. pg_max_conn is by default set to 20, and read_pool_size to 4.

The Postgres connections are a limit on the maximum and the application will dynamically open as many as necessary. If you have a huge amount of concurrency, you might see improvements by increasing pg_max_conn. Keep in mind though, that most data that is used for normal user authentication is cached in memory, so it's possible that it will not help at all. If you want to lower resource usage as much as possible, you might want to consider a lower value for pg_max_conn, even though I would only do this for very tiny Rauthy instances with less than 50 users. The connection pool size for Postgres has a much higher impact than it does for Hiqlite, because of the networking overhead.

For Hiqlite with read_pool_size, you might want to do the same of course. However, the pool is statically built to reduce latency. On the other hand, a higher number of connections will only very slightly increase memory usage. These connections are only for reading data and don't do anything regarding writes. The Hiqlite writer will always be a fixed, single writer connection running on a dedicated thread.

The Hiqlite read pool can be configured in the cluster section:

[cluster]
# The size of the pooled connections for local database reads.
#
# Do not confuse this with a pool size for network databases, as it
# is much more efficient. You can't really translate between them,
# because it depends on many things, but assuming a factor of 10 is
# a good start. This means, if you needed a (read) pool size of 40
# connections for something like a postgres before, you should start
# at a `read_pool_size` of 4.
#
# Keep in mind that this pool is only used for reads and writes will
# travel through the Raft and have their own dedicated connection.
#
# default: 4
# overwritten by: HQL_READ_POOL_SIZE
#read_pool_size = 4

The pg_max_conn is located in the database section:

[database]
# Max DB connections for the Postgres pool.
#
# default: 20
# overwritten by: PG_MAX_CONN
pg_max_conn = 20

log_sync

When using Hiqlite, you can control the Raft Log sync / flush strategy. This has an immediate effect on disk longevity and crash resistance, but of course, also on total throughput.

[cluster]
# Setting for Raft Log syncing / flushing.
#
# This value is probably the most important, depending on your needs.
# It has a huge impact on both performance and consistency.
#
# You can set 3 different levels:
# - immediate
# - immediate_async
# - interval_<time_ms> (e.g. interval_200)
#
# If you run a single instance "Cluster", you most probably want
# `immediate` to have the highest degree of consistency. If set
# to `immediate`, the Raft will block until data has been flushed
# to disk.
# `immediate` has a very huge negative impact on throughput, and
# it puts a lot of stress on your disk, which is important to
# consider for SSDs.
#
# `immediate_async` puts the same amount of stress on your SSD
# and flushes all buffers to disk immediately after a single
# Raft Log was saved. Unlike `immediate`, however, it does not
# wait for completion and directly returns `success` to the
# Raft Engine. You have a tiny bit worse consistency guarantees
# in exchange for basically the same throughput as with `interval`
# syncing.
#
# The `interval_<ms>` option will not flush immediately. Flushes
# will be triggered by an external ticker task every <ms> ms, and
# then only if buffers are dirty, meaning if any data was updated
# since the last sync. This setting has the highest throughput
# and puts the lowest amount of stress on your SSD.
#
# CAUTION: You probably never want to use this setting for a
# single instance, since it may be the case that if you are
# unlucky and your app crashes before buffers are synced, you might
# lose the last few WAL entries. Even though very unlikely in the
# real world (can be force-produced though).
#
# default: immediate_async
# overwritten by: HQL_LOG_SYNC
log_sync = "interval_200"

wal_size + logs_until_snapshot

This applies to Hiqlite only as well. If you only run a small instance, you could save a little bit of memory by adjusting the WAL file size and the threshold when to create a new Snapshot and cleanup Raft Logs. The default values will handle as much throughput as your disk IOPS allow. However, you could tune it down for small instances to e.g.

• wal_size = 262144
• logs_until_snapshot = 1000

[cluster]
# Hiqlite WAL files will always have a fixed size, even when they
# are still "empty", to reduce disk operations while writing. You
# can set the WAL size in bytes. The default value is 2 MiB, while
# the minimum size is 8 kiB.
# The value is given in bytes and should always be a multiple of 
# 4096.
#
# default: 2097152
# overwritten by: HQL_WAL_SIZE
wal_size = 2097152

# Sets the limit when the Raft will trigger the creation of a new
# state machine snapshot and purge all logs that are included in
# the snapshot.
# Higher values can achieve more throughput in really write heavy
# situations but will end up in more disk usage and longer
# snapshot creations / log purges.
#
# default: 10000
# overwritten by: HQL_LOGS_UNTIL_SNAPSHOT
logs_until_snapshot = 10000

This will trigger more often WAL log roll-overs, which of course does more syscalls. But since WAL files are memory-mapped, you can save a little bit of memory at runtime. These values should always be adjusted together. They both have an impact on how many WAL files will exist during normal operation. ideally, you have 2-4 WAL files around during normal operation. At the same time, you should make make these values too small so that Snapshots are not being created more than probably every 15 minutes.

HTTP Server

http_workers

The server.http_workers variable defines the number of HTTP worker threads being spawned. This has a big impact on the amount of memory used. This is especially important when you run Rauthy inside a container on a bigger underlying host with many cores. Rauthy will spawn more workers depending on the total number of cores, and not depending on any container limits you might have set, which it cannot see.

The default value is:

• less than 4 CPU cores -> 1
• 4+ cores -> max(2, cores - MAX_HASH_THREADS - reserve), where reserve is 2 when HIQLITE=true and 1 otherwise

You almost always want to tune this to your needs, it has a big impact on memory! The best idea is probably to use the same formula, but with respect to custom container limits, or whatever you would want Rauthy to use.

[server]
# Limits the amount of HTTP worker threads. This value
# heavily impacts memory usage, even in idle. The default
# values are:
# - less than 4 CPU cores -> 1
# - 4+ cores -> max(2, cores - MAX_HASH_THREADS - reserve)
#   where `reserve` is 2 when `HIQLITE=true` and 1 otherwise.
#
# CAUTION: If you run your instance on a big underlying host,
# you almost always want to manually set an appropriate
# value. Rauthy can only see all available cores and not any
# possibly set container limits. This means if it runs inside
# a container on something like a 96 core host, Rauthy will
# by default spawn very many threads.
#
# overwritten by: HTTP_WORKERS
http_workers = 1

metrics_enable

In newer versions, the metrics_enable is false by default and opt-in. You can enable prometheus metrics with it. An independent HTTP server will be spawned, it will consume additional memory and CPU. Leave it to false if not needed.

[server]
# To enable or disable the additional HTTP server to expose
# the /metrics endpoint.
#
# default: false
# overwritten by: METRICS_ENABLE
metrics_enable = false

swagger_ui_enable

If enable swagger_ui_enable and set it to true, it will consume ~13 MB of additional memory. To reduce overall memory fragmentation further down the road, if enabled, it will be initialized at the very start of the application instead of being lazily initialized. If you don't need the API documentation, leave it to the default, which is false.

[server]
# Can be set to `true` to enable the Swagger UI.
# This will consume ~13mb of additional memory.
#
# default: false
# overwritten by: SWAGGER_UI_ENABLE
swagger_ui_enable = false

Password Hashing

argon2_m_cost + argon2_t_cost + argon2_p_cost + max_hash_threads

Values for password hashing are probably the most important ones to tune overall. They do not only dictate resource usage, but also the strength and security of password hashes. The password hashing will always be the limiting factor, at least as long as not all of your users use Webauthn-only accounts. This book, as well as the Admin UI, have dedicated sections and utilities for these values. Keep in mind to tune them properly.

[hashing]
# Argon2ID hashing parameters. Take a look at the documentation
# for more information:
# https://sebadob.github.io/rauthy/config/argon2.html
# M_COST must never be below 32768 in production
# overwritten by: ARGON2_M_COST
argon2_m_cost = 131072
# T_COST must never be below 1 in production
# overwritten by: ARGON2_T_COST
argon2_t_cost = 4
# P_COST must never be below 2 in production
# overwritten by: ARGON2_P_COST
argon2_p_cost = 8

# Limits the maximum amount of parallel password hashes at the exact same time
# to never exceed system memory while still allowing a good amount of memory
# for the Argon2ID algorithm
#
# CAUTION: You must make sure, that you have at least
# (MAX_HASH_THREADS * ARGON2_M_COST / 1024) + idle memory of your deployment available.
#
# default: 2
# overwritten by: MAX_HASH_THREADS
max_hash_threads = 2

Memory Allocator

Rauthy uses jemalloc under the hood, which you can tune via an environment variable, as long as it's set before the application starts. A default setting is baked into the compiled binary, but when you provide the env var, you can overwrite it. The default is tuned to be just fine for instances with a couple of hundreds of users and focuses more on being efficient rather than providing a high degree of concurrency.

If you have a bigger instance with many thousands or even millions of users, or just a tiny one with probably less than 100, you can optimize it. There is only a small amount of room in terms of lowering memory usage, but a lot of increasing concurrency at the cost of higher memory usage.

I will not go into the details of jemalloc here. If you are interested in this topic, you will find lots of information via the search engine of your choice. I only want to give you recipes that should just work.

Small Instance

If you run a small instance with less than 100 users, and you want to reduce the memory footprint as much as possible, you have two options.

1. Lowest memory usage

This value will probably give you no noticeable performance hit while still providing a low memory usage.

MALLOC_CONF=abort_conf:true,narenas:1,tcache_max:1024,dirty_decay_ms:1000,muzzy_decay_ms:1000

2. Lowest possible memory at all costs.

This will come with a very big performance hit! You should only use it, if you don't care about performance at all. Imo, the performance hit is not worth the small savings compared to the config above.

MALLOC_CONF=abort_conf:true,narenas:1,tcache:false,dirty_decay_ms:0,muzzy_decay_ms:0

Medium Instance

If you run a medium instance with up to 500-1000 users, you are probably just fine with the defaults. Stick to them. Just for reference, the currently used default config is this:

MALLOC_CONF=abort_conf:true,narenas:8,tcache_max:4096,dirty_decay_ms:5000,muzzy_decay_ms:5000

Big Instance

A big instance is one with more than at least 1000 users. In this case, you might not get the desired performance, especially if you have a higher value for MAX_HASH_THREADS or HTTP_WORKERS. Most requests are so small, that they almost entirely fit in the thread-local cache for the allocator, but if dynamic brotli compression kicks in, memory from an allocator arena will be necessary most of the time. Because Rauthy does not need the arena's that often, the default value of 4 is too low in such a case. You should set narenas from the string below at least equal to the amount of CPU cores your Rauthy instance is assigned to. Depending on the amount or concurrent logins, you may set narenas to 2-4x CPU cores at the cost of higher memory usage.

MALLOC_CONF=abort_conf:true,narenas:16,tcache_max:16384,dirty_decay_ms:10000,muzzy_decay_ms:10000

Open End

For any instance with basically an open end of users, or if you have a very high degree of concurrent logins (or you just don't care about low memory usage and only about max performance), set narenas to 4x your CPU cores (higher values will start to have a negative impact). This config will let you scale into millions of users easily.

MALLOC_CONF=abort_conf:true,narenas:64,tcache_max:32768,dirty_decay_ms:30000,muzzy_decay_ms:30000