Track and expose node capabilities per connection by hjohn · Pull Request #529 · AxonIQ/axonserver-connector-java

hjohn · 2026-10-20T13:56:56Z

Adds AxonServerConnection.supports(String capability), backed by the capabilities reported in PlatformInfo on every (re)connect in AxonServerManagedChannel.

Lets a client check in advance whether the node it's currently connected to supports an optional RPC/behavior, rather than calling it and reacting to UNIMPLEMENTED. Re-evaluated on every reconnect, so gaining/losing a capability (e.g. after moving to a different cluster node) takes effect immediately rather than being cached for the connection's lifetime.

A redirect is now followed to completion. Previously the client called GetPlatformServer and, on a redirect, simply opened the stream against the node it was pointed at without ever asking it anything. It now re-runs the handshake against each node it is sent to until one answers for itself, with a hop limit. Since every answer reports the capabilities of the node that produced it, the client holds the capabilities of whichever node it ends up on - including when it stops following redirects and stays put, because following one more hop would land it on an unqueried node again.

This happens inside connect(), before the connection is handed out, so there is no window in which the connection is usable with capabilities still unknown, and the set is fixed for as long as that connection holds.

Also exposes the two RPCs that supersede the snapshotted-source path: DcbEventChannel.sourceWithSnapshot and SnapshotChannel.findLastSnapshot. The source(SnapshottedSourceRequest) overload is deprecated, since Axon Server no longer implements the RPC behind it.

Depends on AxonIQ/axon-server-api#80 for PlatformInfo.capabilities, and on AxonIQ/axon-server-api#78 for the new RPCs.

First consumer: AxoniqFramework's AxonServerEventStorageEngine, in a followup PR.

CLAassistant · 2026-10-20T14:07:03Z

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hatzlj · 2026-10-20T15:02:12Z

+     * either does not support it, or has not advertised any capabilities at all (e.g. because it predates capability
+     * negotiation)
+     */
+    boolean supports(String capability);


Where is the list of available capabilities maintained? A hint in the javadoc where to find the list of available capabilities would be helpful for users of that API.

Agreed. We should have some notion of where these are given. A reference back to Axon Server may suffice, that'll likely hint people to check the Reference Guide for this.

smcvb

Frankly, I think this is fine as is. We can imagine all kinds of "nice" enumerations of option we'd have, but we (1) wouldn't have the list right now at all and (2) that'll tie us in to potential breaking API changes. By using a String for the capability, we have a lot of flexibility. Granted, I agree with @hatzlj, that some form of listing, somewhere, would be important.

smcvb · 2026-10-23T08:01:13Z

+     * either does not support it, or has not advertised any capabilities at all (e.g. because it predates capability
+     * negotiation)
+     */
+    boolean supports(String capability);


Agreed. We should have some notion of where these are given. A reference back to Axon Server may suffice, that'll likely hint people to check the Reference Guide for this.

smcvb

Some minor pointers out of curiosity

smcvb · 2026-10-26T15:34:09Z

    }

    @Override
+    @Deprecated


Curious: why deprecate this? I understand it's recommended to use the other, but there's not anything inherently wrong with this API, right?

There is, in 2026.1.x (until we release a fixed version) it will SKIP a potential matching event when using this callback. That's what broke platform for Mitchel. I don't recommend having a mix of fixed and unfixed versions.

smcvb · 2026-10-26T15:37:10Z

     * @return the response containing an optional snapshot, events to source a model, and a consistency marker to be
     * used when trying to append new events to the event store
+     * @deprecated superseded by {@link #sourceWithSnapshot(SourceWithSnapshotRequest)}. Axon Server no longer
+     * implements the RPC behind this method and answers it with {@code UNIMPLEMENTED}; it resumed sourcing one past


Ooow didn't know we would be going the route of dropping the regular source operation. Does @m1l4n54v1c / @MGathier / @trimoq agree with this?

This is not the regular source operation, this is the source with snapshot which is broken and which we disabled in the AF 5.4.1 update. I think it is best to let it be superceded with one that works correctly rather than trying to fix it.

smcvb · 2026-10-26T15:38:47Z

-
-        return result.get();
-    }
+/*


This is aa...interesting change. Not sure what happened with your commits here, @hjohn.

Sorry, you're so fast ;) Didn't even get to check this yet. Will fix.

The line endings were changed. Original had CRLF (which is incorrect).

You can toggle showing white space changes in Github (temporarily) with the gear button next to the Submit Review button. With that off, you can see the true diff.

Adds AxonServerConnection.supports(String capability), backed by the capabilities reported in PlatformInfo on every (re)connect. A redirect is now followed to completion: the node we are sent to is asked for its own PlatformInfo in turn, until one answers for itself. Previously the client took the redirect on trust and opened the stream against a node it had never spoken to. Each answer reports the capabilities of the node that produced it, so whichever node we end up on we hold its capabilities - including when we stop following redirects and stay where we are, since following one more hop would land us on an unqueried node again. This all happens inside connect(), before the connection is handed out, so the set is known up front and fixed for as long as it holds. Also adds DcbEventChannel.sourceWithSnapshot and SnapshotChannel.findLastSnapshot for the superseding Axon Server RPCs, and deprecates the source(SnapshottedSourceRequest) overload, whose RPC is no longer implemented.

hjohn requested a review from a team as a code owner October 20, 2026 13:56

hjohn requested review from MGathier, m1l4n54v1c and trimoq and removed request for a team October 20, 2026 13:56

hjohn force-pushed the feature/node-capabilities branch from c54da83 to 61dd82a Compare October 20, 2026 14:05

hjohn mentioned this pull request Oct 20, 2026

Make AxonServerEventStorageEngine capability-aware AxonIQ/axoniq-framework#683

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hatzlj reviewed Oct 20, 2026

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hjohn self-assigned this Oct 22, 2026

hjohn added Type: Enhancement Priority 1: Must labels Oct 22, 2026

smcvb added this to the Axon Server Connector for Java 2026.1.2 milestone Oct 23, 2026

smcvb approved these changes Oct 23, 2026

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hjohn force-pushed the feature/node-capabilities branch 2 times, most recently from ac152f9 to 22fdcaa Compare October 26, 2026 14:42

smcvb reviewed Oct 26, 2026

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hjohn force-pushed the feature/node-capabilities branch 2 times, most recently from c8b1379 to d65a8ad Compare October 27, 2026 15:58

hjohn force-pushed the feature/node-capabilities branch from d65a8ad to 34ee892 Compare October 27, 2026 16:14

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