<#import "/templates/guide.adoc" as tmpl>
<#import "/templates/kc.adoc" as kc>
<#import "/templates/options.adoc" as opts>
<#import "/templates/links.adoc" as links>

<@tmpl.guide
title="Configuring distributed caches"
summary="Understand how to configure the caching layer"
includedOptions="cache cache-*">

{project_name} is designed for high availability and multi-node clustered setups.
The current distributed cache implementation is built on top of https://infinispan.org[Infinispan], a high-performance, distributable in-memory data grid.

== Enable distributed caching
When you start {project_name} in production mode, by using the `start` command, caching is enabled and all {project_name} nodes in your network are discovered.

By default, caches are using a UDP transport stack so that nodes are discovered using IP multicast transport based on UDP. For most production environments, there are better discovery alternatives to UDP available. {project_name} allows you to either choose from a set of pre-defined default transport stacks, or to define your own custom stack, as you will see later in this {section}.

To explicitly enable distributed infinispan caching, enter this command:

<@kc.start parameters="--cache=ispn"/>

When you start {project_name} in development mode, by using the `start-dev` command, {project_name} uses only local caches and distributed caches are completely disabled by implicitly setting the `--cache=local` option.
The `local` cache mode is intended only for development and testing purposes.

== Configuring caches
{project_name} provides a cache configuration file with sensible defaults located at `conf/cache-ispn.xml`.

The cache configuration is a regular https://infinispan.org/docs/stable/titles/configuring/configuring.html[Infinispan configuration file].

The following table gives an overview of the specific caches {project_name} uses.
You configure these caches in `conf/cache-ispn.xml`:

[%autowidth]
|===
|Cache name|Cache Type|Description

|realms|Local|Cache persisted realm data
|users|Local|Cache persisted user data
|authorization|Local|Cache persisted authorization data
|keys|Local|Cache external public keys
|work|Replicated|Propagate invalidation messages across nodes
|authenticationSessions|Distributed|Caches authentication sessions, created/destroyed/expired during the authentication process
|sessions|Distributed|Cache persisted user session data
|clientSessions|Distributed|Cache persisted client session data
|offlineSessions|Distributed|Cache persisted offline user session data
|offlineClientSessions|Distributed|Cache persisted offline client session data
|loginFailures|Distributed|keep track of failed logins, fraud detection
|actionTokens|Distributed|Caches action Tokens
|===

=== Cache types and defaults

.Local caches
{project_name} caches persistent data locally to avoid unnecessary round-trips to the database.

The following data is kept local to each node in the cluster using local caches:

* *realms* and related data like clients, roles, and groups.
* *users* and related data like granted roles and group memberships.
* *authorization* and related data like resources, permissions, and policies.
* *keys*

Local caches for realms, users, and authorization are configured to hold up to 10,000 entries per default.
The local key cache can hold up to 1,000 entries per default and defaults to expire every one hour.
Therefore, keys are forced to be periodically downloaded from external clients or identity providers.

In order to achieve an optimal runtime and avoid additional round-trips to the database you should consider looking at
the configuration for each cache to make sure the maximum number of entries is aligned with the size of your database. More entries
you can cache, less often the server needs to fetch data from the database. You should evaluate the trade-offs between memory utilization and performance.

.Invalidation of local caches
Local caching improves performance, but adds a challenge in multi-node setups.

When one {project_name} node updates data in the shared database, all other nodes need to be aware of it, so they invalidate that data from their caches.

The `work` cache is a replicated cache and used for sending these invalidation messages. The entries/messages in this cache are very short-lived,
and you should not expect this cache growing in size over time.

.Authentication sessions
Authentication sessions are created whenever a user tries to authenticate. They are automatically destroyed once the authentication process
completes or due to reaching their expiration time.

The `authenticationSessions` distributed cache is used to store authentication sessions and any other data associated with it
during the authentication process.

By relying on a distributable cache, authentication sessions are available to any node in the cluster so that users can be redirected
to any node without losing their authentication state. However, production-ready deployments should always consider session affinity and favor redirecting users
to the node where their sessions were initially created. By doing that, you are going to avoid unnecessary state transfer between nodes and improve
CPU, memory, and network utilization.

.User sessions
Once the user is authenticated, a user session is created. The user session tracks your active users and their state so that they can seamlessly
authenticate to any application without being asked for their credentials again. For each application, the user authenticates with a client session, so that the server can track the applications the user is authenticated with and their state on a per-application basis.

User and client sessions are automatically destroyed whenever the user performs a logout, the client performs a token revocation, or due to reaching their expiration time.

The session data are stored in the database by default and loaded on-demand to the following caches:

* sessions
* clientSessions

By relying on a distributable cache, cached user and client sessions are available to any node in the cluster so that users can be redirected
to any node without the need to load session data from the database. However, production-ready deployments should always consider session affinity and favor redirecting users
to the node where their sessions were initially created. By doing that, you are going to avoid unnecessary state transfer between nodes and improve
CPU, memory, and network utilization.

These in-memory caches for user sessions and client sessions are limited to, by default, 10000 entries per node which reduces the overall memory usage of {project_name} for larger installations.
The internal caches will run with only a single owner for each cache entry.
Consider trade-off between memory consumption and the database utilization and set different sizes for the caches, edit {project_name}'s cache config file (`conf/cache-ispn.xml`) to set a `+<memory max-count="..."/>+` for those caches.

.Volatile user sessions

By default, user sessions are stored in the database and loaded on-demand to the cache.
It is possible to configure {project_name} to store user sessions in the cache only and minimize the database utilization.

Since all the sessions in this setup are stored in-memory, there are two side effects related to this:
* Losing sessions on all Keycloak nodes restart
* Increased memory consumption

Follow these steps to enable this setup:

1. Since the cache is the only source of truth for user and client sessions, configure caches to not limit the number of entries and to replicate each entry to at least two nodes. To do so, edit {project_name}'s cache config file (`conf/cache-ispn.xml`) for caches `sessions` and `clientSessions` with the following update:
+
--
* Remove the `+<memory max-count="..."/>+`
* Change `owners` attribute of the `distributed-cache` tag to 2 or more
--
+
An example of the resulting configuration for the `sessions` cache would look as follows.
+
[source,xml]
----
<distributed-cache name="sessions" owners="2">
    <expiration lifespan="-1"/>
</distributed-cache>
----
2. Disable `persistent-user-sessions` feature using the following command:
+
----
bin/kc.sh start --features-disabled=persistent-user-sessions ...
----

[NOTE]
====
Disabling `persistent-user-sessions` is not possible when `multi-site` feature is enabled.
====

.Offline user sessions
As an OpenID Connect Provider, the server is also capable of authenticating users and issuing offline tokens. Similarly to regular user and client sessions,
when an offline token is issued by the server upon successful authentication, the server also creates an offline user session and an offline client session.

The following caches are used to store offline sessions:

* offlineSessions
* offlineClientSessions

Similarly to regular user and client sessions caches, also the offline user and client session caches are limited to 10000 entries per node by default. Items which are evicted from the memory will be loaded on-demand from the database when needed.
Consider trade-off between memory consumption and the database utilization and set different sizes for the caches, edit {project_name}'s cache config file (`conf/cache-ispn.xml`) to set a `+<memory max-count="..."/>+` for those caches.

.Password brute force detection
The `loginFailures` distributed cache is used to track data about failed login attempts.
This cache is needed for the Brute Force Protection feature to work in a multi-node {project_name} setup.

.Action tokens
Action tokens are used for scenarios when a user needs to confirm an action asynchronously, for example in the emails sent by the forgot password flow.
The `actionTokens` distributed cache is used to track metadata about action tokens.

=== Configuring cache maximum size
In order to reduce memory usage, it's possible to place an upper bound on the number of entries which are stored in a given
cache. To specify an upper bound of on a cache, you must provide the following command line argument
`--cache-embedded-$\{CACHE_NAME}-max-count=`, with `$\{CACHE_NAME}` replaced with the name of the cache you would like to
apply the upper bound to. For example, to apply an upper-bound of `1000` to the `offlineSessions` cache you would configure
`--cache-embedded-offline-sessions-max-count=1000`. An upper bound can not be defined on the following caches:
`actionToken`, `authenticationSessions`, `loginFailures`, `work`.

=== Configuring caches for availability

Distributed caches replicate cache entries on a subset of nodes in a cluster and assigns entries to fixed owner nodes.

Each distributed cache, that is a primary source of truth of the data (`authenticationSessions`, `loginFailures` and `actionTokens`) has two owners per default, which means that two nodes have a copy of the specific cache entries.
Non-owner nodes query the owners of a specific cache to obtain data.
When both owner nodes are offline, all data is lost.

The default number of owners is enough to survive 1 node (owner) failure in a cluster setup with at least three nodes. You are free
to change the number of owners accordingly to better fit into your availability requirements. To change the number of owners, open `conf/cache-ispn.xml` and change the value for `owners=<value>` for the distributed caches to your desired value.

=== Specify your own cache configuration file

To specify your own cache configuration file, enter this command:

<@kc.start parameters="--cache-config-file=my-cache-file.xml"/>

The configuration file is relative to the `conf/` directory.

=== CLI options for remote server

For configuration of {project_name} server for high availability and multi-node clustered setup there was introduced following CLI options `cache-remote-host`, `cache-remote-port`, `cache-remote-username` and `cache-remote-password` simplifying configuration within the XML file.
Once any of declared CLI parameters are present, it is expected there is no configuration related to remote store present in the XML file.

==== Connecting to an insecure Infinispan server

WARNING: Disabling security is not recommended in production!

In a development or test environment, it is easier to start an unsecured Infinispan server.
For these use case, the CLI options `cache-remote-tls-enabled` disables the encryption (TLS) between {project_name} and {jdgserver_name}.
{project_name} will fail to start if the {jdgserver_name} server is configured to accept only encrypted connections.

The CLI options `cache-remote-username` and `cache-remote-password` are optional and, if not set, {project_name} will connect to the {jdgserver_name} server without presenting any credentials.
If the {jdgserver_name} server has authentication enabled, {project_name} will fail to start.

== Transport stacks
Transport stacks ensure that distributed cache nodes in a cluster communicate in a reliable fashion.
{project_name} supports a wide range of transport stacks:

<@opts.expectedValues option="cache-stack"/>

To apply a specific cache stack, enter this command:

<@kc.start parameters="--cache-stack=<stack>"/>

The default stack is set to `udp` when distributed caches are enabled.

=== Available transport stacks

The following table shows transport stacks that are available without any further configuration than using the `--cache-stack` build option:

[%autowidth]
|===
|Stack name|Transport protocol|Discovery

|tcp|TCP|MPING (uses UDP multicast).
|udp|UDP|UDP multicast
|===

The following table shows transport stacks that are available using the `--cache-stack` runtime option and a minimum configuration:

[%autowidth]
|===
|Stack name|Transport protocol|Discovery

|kubernetes|TCP|DNS_PING (requires `-Djgroups.dns.query=<headless-service-FQDN>` to be added to JAVA_OPTS or JAVA_OPTS_APPEND environment variable).
|===

=== Additional transport stacks
The following table shows transport stacks that are supported by {project_name}, but need some extra steps to work.
Note that _none_  of these stacks are Kubernetes / OpenShift stacks, so no need exists to enable the `google` stack if you want to run {project_name} on top of the Google Kubernetes engine.
In that case, use the `kubernetes` stack.
Instead, when you have a distributed cache setup running on AWS EC2 instances, you would need to set the stack to `ec2`, because ec2 does not support a default discovery mechanism such as UDP.

[%autowidth]
|===
|Stack name|Transport protocol|Discovery

|ec2|TCP|NATIVE_S3_PING
|google|TCP|GOOGLE_PING2
|azure|TCP|AZURE_PING
|===

Cloud vendor specific stacks have additional dependencies for {project_name}.
For more information and links to repositories with these dependencies, see the https://infinispan.org/docs/dev/titles/embedding/embedding.html#jgroups-cloud-discovery-protocols_cluster-transport[Infinispan documentation].

To provide the dependencies to {project_name}, put the respective JAR in the `providers` directory and build {project_name} by entering this command:

<@kc.start parameters="--cache-stack=<ec2|google|azure>"/>

=== Custom transport stacks
If none of the available transport stacks are enough for your deployment, you are able to change your cache configuration file
and define your own transport stack.

For more details, see https://infinispan.org/docs/stable/titles/server/server.html#using-inline-jgroups-stacks_cluster-transport[Using inline JGroups stacks].

.defining a custom transport stack
[source]
----
<jgroups>
    <stack name="my-encrypt-udp" extends="udp">
    <SSL_KEY_EXCHANGE keystore_name="server.jks"
        keystore_password="password"
        stack.combine="INSERT_AFTER"
        stack.position="VERIFY_SUSPECT2"/>
        <ASYM_ENCRYPT asym_keylength="2048"
        asym_algorithm="RSA"
        change_key_on_coord_leave = "false"
        change_key_on_leave = "false"
        use_external_key_exchange = "true"
        stack.combine="INSERT_BEFORE"
        stack.position="pbcast.NAKACK2"/>
    </stack>
</jgroups>

<cache-container name="keycloak">
    <transport lock-timeout="60000" stack="my-encrypt-udp"/>
    ...
</cache-container>
----

By default, the value set to the `cache-stack` option has precedence over the transport stack you define in the cache configuration file.
If you are defining a custom stack, make sure the `cache-stack` option is not used for the custom changes to take effect.

== Securing cache communication
The current Infinispan cache implementation should be secured by various security measures such as RBAC, ACLs, and transport stack encryption.

JGroups handles all the communication between {project_name} server, and it supports Java SSL sockets for TCP communication.
{project_name} uses CLI options to configure the TLS communication without having to create a customized JGroups stack or modifying the cache XML file.

To enable TLS, `cache-embedded-mtls-enabled` must be set to `true`.
It requires a keystore with the certificate to use: `cache-embedded-mtls-key-store-file` sets the path to the keystore, and `cache-embedded-mtls-key-store-password` sets the password to decrypt it.
The truststore contains the valid certificates to accept connection from, and it can be configured with `cache-embedded-mtls-trust-store-file` (path to the truststore), and `cache-embedded-mtls-trust-store-password` (password to decrypt it).
To restrict unauthorized access, use a self-signed certificate for each {project_name} deployment.

For JGroups stacks with `UDP` or `TCP_NIO2`, see the http://jgroups.org/manual5/index.html#ENCRYPT[JGroups Encryption documentation] on how to set up the protocol stack.

For more information about securing cache communication, see the https://infinispan.org/docs/stable/titles/security/security.html#[Infinispan security guide].

== Exposing metrics from caches

Metrics from caches are automatically exposed when the metrics are enabled.

To enable histograms for the cache metrics, set `cache-metrics-histograms-enabled` to `true`.
While these metrics provide more insights into the latency distribution, collecting them might have a performance impact, so you should be cautious to activate them in an already saturated system.

<@kc.start parameters="--metrics-enabled=true --cache-metrics-histograms-enabled=true"/>

For more details about how to enable metrics, see <@links.server id="configuration-metrics"/>.

</@tmpl.guide>
