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Set up Cluster Bootstrap with MongoDB discovery

This guide will help you use MongoDB as a discovery mechanism for bootstrapping an Akka cluster

Step 0: Add dependency

You will need to add this to pom.xml:

<dependency>
    <groupId>com.iconsolutions.ipf.core.discovery</groupId>
    <artifactId>akka-discovery-mongodb-plugin</artifactId>
</dependency>

To find the latest version, you can use this Nexus query.

Step 1: Enable Akka Cluster Bootstrap and Use MongoDB

Add this snippet to your configuration (application.conf):

akka {
  extensions = ["akka.management.cluster.bootstrap.ClusterBootstrap"]
  discovery {
    method = akka-mongodb
    akka-mongodb.uri = ${ipf.mongodb.url} # or use an actual MongoDB URI if not using this with IPF
  }
  management.cluster.bootstrap {
    contact-point.filter-on-fallback-port=false
  }
}

Step 2: Verify

When starting up your application, you should check that indexes are created and that the service registers itself.

Look for these lines in the log:

[INFO] [04/26/2023 20:43:55.668] Ensured indexes on Akka Discovery MongoDB ([akka-discovery-mongodb-1])
[INFO] [04/26/2023 20:43:55.663] Registered self with service name 8cc4d63b-09c8-4fca-9668-b11e6d00e75a and host:port 127.0.1.1:8558: AcknowledgedUpdateResult{matchedCount=0, modifiedCount=0, upsertedId=BsonObjectId{value=64497efb0b510545dbb89377}}

Note that both of these pieces of functionality can be disabled. See below.

You should now also be able to navigate to the Akka Management HTTP service (the default being 127.0.1.1:8558) and observe that all nodes of the same type and that are using the same discovery method should be in a cluster together.

Appendix A: Default Configuration

The table below describes the default configuration that ships with the library:

Config key Description Default value

akka.discovery.akka-mongodb.uri

The MongoDB URI to use to connect to the database.

Set the value of this field if not using the plugin from within IPF or if not intending to use the same database as IPF.

Honours the global ipf.mongodb.url property.

ipf.mongodb.url if used within IPF, mongodb://localhost:27017/ipf otherwise

akka.discovery.akka-mongodb.collection

The name of the collection to store discovery data into

akka-discovery-mongodb

akka.discovery.akka-mongodb.register-self

Should this node register itself in the database?

true

akka.discovery.akka-mongodb.create-indexes

Should akka-discovery-mongodb create indexes for itself?

Disable this if the database user is not granted the createIndex action.

Honours the global IPF ipf.mongodb.create-indexes override.

ipf.mongodb.create-indexes if set, true otherwise

akka.discovery.akka-mongodb.commit-quorum

The commit quorum to use when creating the index for Akka Discovery MongoDB.

Honours the global IPF ipf.mongodb.commit-quorum override.

ipf.mongodb.commit-quorum if set, votingMembers otherwise

akka.discovery.akka-mongodb.updater.enabled

Should the Updater run?

true

akka.discovery.akka-mongodb.updater.initial-delay

Initial delay before the Updater starts updating its entry’s lastUpdated value

30 seconds

akka.discovery.akka-mongodb.updater.initial-delay

How often to update the lastUpdated value

30 seconds

akka.discovery.akka-mongodb.updater.expire-entries-older-than

The expireAfter value of the MongoDB TTL index that is created

30 minutes

akka.discovery.akka-mongodb.set-ssl-context

Whether to enable SSL support.

Setting this to true will require setting some of the ssl-context settings below.

Honours the global ipf.mongodb.set-ssl-context override.

ipf.mongodb.set-ssl-context if set

akka.discovery.akka-mongodb.ssl-context.key-store-type

Type of the key store.

Honours the global ipf.mongodb.ssl-context.key-store-type override.

ipf.mongodb.ssl-context.key-store-type if set

akka.discovery.akka-mongodb.ssl-context.key-store-location

Path to the key store that holds the SSL certificate (typically a jks file).

Honours the global ipf.mongodb.ssl-context.key-store-location override.

ipf.mongodb.ssl-context.key-store-location if set

akka.discovery.akka-mongodb.ssl-context.key-store-password

Password used to access the key store.

Honours the global ipf.mongodb.ssl-context.key-store-password override.

ipf.mongodb.ssl-context.key-store-password if set

akka.discovery.akka-mongodb.ssl-context.key-password

Password used to access the key in the key store.

Honours the global ipf.mongodb.ssl-context.key-password override.

ipf.mongodb.ssl-context.key-password if set

akka.discovery.akka-mongodb.ssl-context.trust-store-type

Type of the trust store.

Honours the global ipf.mongodb.ssl-context.trust-store-type override.

ipf.mongodb.ssl-context.trust-store-type if set

akka.discovery.akka-mongodb.ssl-context.trust-store-location

Path to the trust store that holds the SSL certificate.

Honours the global ipf.mongodb.ssl-context.trust-store-location override.

ipf.mongodb.ssl-context.trust-store-location if set

akka.discovery.akka-mongodb.ssl-context.trust-store-password

Password used to access the trust store.

Honours the global ipf.mongodb.ssl-context.trust-store-password override.

ipf.mongodb.ssl-context.trust-store-password if set

Note that there is also general Akka Cluster Bootstrap config that you might wish to tweak. The general Akka Cluster Bootstrap documentation can be found here.