akka/akka-core

Cluster sharding: Expose entity ID to the sharded actor

Open

#24,053 opened on Nov 23, 2017

View on GitHub
 (17 comments) (1 reaction) (0 assignees)Scala (13,277 stars) (3,547 forks)batch import
help wantednice-to-have (low-prio)t:cluster-sharding

Description

Apologies in advance if this issue was brought up in the past. I tried to search for it, but couldn't find anything...

Currently, sharded actors don't have access to their entity identifier. The example in the docs uses self.path.name, but that is URL-encoded and not the actual ID. On top of that, this seems to be an implementation detail - the encoded ID happens to be what the shard uses for the actor name. At the same time, it is obvious that adding an Actor.entityId method is not a good solution (actors don't know whether or not they're sharded).

So I suggest modifying the ClusterSharding.start (or adding another API next to it) so that instead of taking Props as a parameter, it would take a String => Props function that would get invoked with the entity ID. What do you think?

(Of course, I wouldn't mind doing a PR for it, if there's interest)

Contributor guide

Tech stack
scala
Domain
backend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
ScalaAkkaCluster Sharding
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
The issue proposes modifying ClusterSharding.start to accept a String => Props function instead of Props, enabling sharded actors to access their entity ID. Implementation would involve updating the API in akka cluster sharding, likely in ClusterSharding.scala, and ensuring backward compatibility. The discussion suggests no breaking changes if done carefully. A PR can be based on the suggestion, adding a new overloaded method. Testing should cover entity ID passing and URL encoding behavior.