Keycloak 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.
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. Keycloak 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}.
When you start Keycloak in development mode, by using the `start-dev` command, Keycloak uses only local caches and distributed caches are completely disabled by implicitly setting the `--cache=local` option.
The following table gives an overview of the specific caches Keycloak uses.
You configure these caches in `conf/cache-ispn.xml`:
|====
|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|Caches user sessions, created upon successful authentication and destroyed during logout, token revocation, or due to expiration
|clientSessions|Distributed|Caches client sessions, created upon successful authentication to a specific client and destroyed during logout, token revocation, or due to expiration
|offlineSessions|Distributed|Caches offline user sessions, created upon successful authentication and destroyed during logout, token revocation, or due to expiration
|offlineClientSessions|Distributed|Caches client sessions, created upon successful authentication to a specific client and destroyed during logout, token revocation, or due to expiration
|loginFailures|Distributed|keep track of failed logins, fraud detection
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.
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
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
is created too, 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 following caches are used to store both user and client sessions:
By relying on a distributable cache, user and client sessions are available to any node in the cluster so that users can be redirected
to any node without loosing their 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.
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 a user and client sessions. However, due to the nature
of offline tokens, offline sessions are handled differently as they are long-lived and should survive a complete cluster shutdown. Because of that, they are also persisted to the database.
The following caches are used to store offline sessions:
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.
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.
The following table shows transport stacks that are supported by Keycloak, 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 Keycloak 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`.
Cloud vendor specific stacks have additional dependencies for Keycloak.
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].
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].
The current Infinispan cache implementation should be secured by various security measures such as RBAC, ACLs, and Transport stack encryption. For more information about securing cache communication, see the https://infinispan.org/docs/dev/titles/security/security.html#[Infinispan security guide].
To enable global metrics for all caches within the `cache-container`, you need to change your cache configuration file (e.g.: `conf/cache-ispn.xml`) to enable `statistics` at the `cache-container` level as follows:
