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NatsPublish (CodeActivity) publishes a UTF-8 body to a subject with optional Nats-Msg-Id dedup and ExpectedStream assertion. NatsTrigger (Trigger<string>) starts a workflow per message on a specified stream/subject. A single BackgroundService scans the trigger store for indexed NatsTriggers, groups by (stream, subject), and runs one durable pull consumer per pair with Explicit ack, so multiple Elsa instances share the workload at-least-once. A mediator handler on WorkflowTriggersIndexed refreshes subscriptions when workflows are published. Wired via Nats:Url/User/Password (env-var overrides Nats__*, or short NATS_URL/NATS_USER/NATS_PASSWORD fallbacks). Uses the NATS.Net v2 client so wss:// works transparently.
Elsa Custom Server
Custom Elsa Workflows API server. Extends stock Elsa 3.x with our own activities.
Where activities live
src/Elsa.CustomServer/Activities/*.cs — anything marked [Activity(...)] under this
folder is auto-registered via AddActivitiesFrom<Program>() in Program.cs.
To add a new node type in the Studio designer:
- Drop a new file under
Activities/. - Inherit from
CodeActivity,CodeActivity<T>, orActivityfor triggerable ones. - Rebuild and redeploy — Studio picks it up automatically the next time it fetches the activity descriptors.
Example — see Activities/Shout.cs.
Local run
dotnet run --project src/Elsa.CustomServer
Listens on http://localhost:8080; API root is /elsa/api.
Docker
docker build -t elsa-custom-server .
docker run --rm -p 8080:8080 \
-e Identity__Tokens__SigningKey="$(openssl rand -base64 64)" \
elsa-custom-server
Deployment
Coolify builds this image from the Dockerfile at repo root when the app is created
with build_pack: "dockerfile". The Studio (separate container running the stock
elsaworkflows/elsa-studio-v3 image) needs its BACKEND__URL env var pointed at
this server's /elsa/api.