Cannot configure Ebean read replica with Play configuration #566

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1. rbygrave commented on Jul 28, 2025

   

   rbygrave

   on Jul 28, 2025

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   This has been crossed posted, refer to ebean-orm/ebean#3659
2. risenhoover

   closed this as completedon Jul 28, 2025
3. risenhoover

   reopened this on Jul 29, 2025
4. risenhoover commented on Jul 29, 2025

   

   risenhoover

   on Jul 29, 2025

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   Based on conversations with @rbygrave in the ticket references above, it appears that the play-ebean package does not honor the readonlyUrl configuration item and properly build a read replica. I have reopened this issue since it seems important.
5. risenhoover

   changed the title [-]Cannot configure readonly database with play configuration[/-] [+]Cannot configure Ebean read replica with Play configuration[/+] on Jul 29, 2025
6. certara-gdoenlen commented on Mar 16, 2026

   

   certara-gdoenlen

   on Mar 16, 2026

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   @mkurz is this something you could maybe give guidance on? I was hoping to use the readReplica feature for our system.
   @risenhoover did you ever find a solution?
7. mkurz

   closed this as completedin #892on Oct 8, 2026
8. mkurz commented on Oct 8, 2026

   

   mkurz

   on Oct 8, 2026

   Last edited by mkurz

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   This got closed by

   • Support read replicas via play.ebean.readOnlyDatasources #892
   • (backports: [8.x] Support read replicas via play.ebean.readOnlyDatasources #893 for 8.x, [7.x] Support read replicas via play.ebean.readOnlyDatasources #894 for 7.x).

   Before it got released, its setting was renamed in

   • Allow turning evolutions script generation on or off per Ebean server #901 ([8.x] Allow turning evolutions script generation on or off per Ebean server #902, sbt 2.0.0 (was 1.12.13) #769

   so with the next releases you configure a read replica like this:

   db.default.url = "jdbc:postgresql://primary-host/app"
   db.replica.url = "jdbc:postgresql://replica-host/app"
   db.replica.hikaricp.readOnly = true
   
   ebean.default = ["models.*"]
   play.ebean.db.default.readOnlyDatasource = "replica"

   The replica is just an additional Play database, so credentials, URL formats like postgres://... and the hikaricp settings work as usual. It becomes the read-only data source of the Ebean server: queries outside of transactions, as well as explicitly read-only transactions (e.g. TxScope.required().setReadOnly(true)), run against the replica, everything else against the primary. Ebean supports one read-only data source per Ebean server, so for multiple replicas use a JDBC URL listing all of them (if the driver supports it, e.g. PostgreSQL's loadBalanceHosts and targetServerType), a load balancer or a reader endpoint.

   Why the attempts above didn't work

   • db.default.readOnlyUrl: that's not a Play setting, so it got silently ignored. Play Ebean only ever handed the main connection pool to Ebean.
   • db.readonly with readOnlyDatabase=true: Play Ebean only creates an Ebean server for databases listed in ebean.*, and readOnlyDatabase is an Ebean setting, not a Play one. Besides, that would be a separate Ebean server, not a read replica used by the default one.
   • readOnlyUrl in Ebean's own properties: Ebean then creates a connection pool of its own for the read-only queries, and copies the user and password from its own main data source configuration. That one is empty with Play Ebean though, as Play provides the main connection pool, so it fails with DataSource user is not set?.
   • The ServerConfigStartup: the NullPointerException comes from the postgres://... URL. Play converts that URL format, but Ebean's DataSourceBuilder needs a JDBC URL (jdbc:postgresql://host:5432/db). The PostgreSQL driver returns no connection for other URLs, which Ebean doesn't expect.

   Until the next release

   With the current releases, either of these works:

   • datasource.default.readOnlyUrl together with datasource.default.username and datasource.default.password in Ebean's own configuration, e.g. conf/application.yaml.
   • A ServerConfigStartup with a JDBC URL and the credentials. It has to be covered by an ebean. config line, e.g. by putting it into the models package, otherwise Ebean doesn't pick it up:

   public class ReadReplicaStartup implements ServerConfigStartup {
     @Override
     public void onStart(DatabaseBuilder config) {
       DataSourceBuilder.Settings replica = DataSourceBuilder.create().settings();
       replica.driver("org.postgresql.Driver");
       replica.url("jdbc:postgresql://replica-host:5432/app");
       replica.username("...");
       replica.password("...");
       config.readOnlyDataSourceBuilder(replica);
     }
   }

   The docs now have a "Using a read replica" section.