How a capsule becomes a running service

You write a capsule, publish it to a node, and deploy it under a service name. Each call to that service creates a new activation. These names describe different steps, which matters when you update a program or recover a lost response.

Follow one greeting request

Imagine a capsule with a greet function that returns Hello, Ada!:

1. Build the capsule. The result is a WebAssembly component and its contract: a description of the inputs and outputs.
2. Publish it. The node checks the submitted program and returns a publication ID. That ID identifies this admitted publication in your tenant.
3. Deploy it. A deployment associates a service such as examples/greeting with the publication that should answer its calls.
4. Invoke it. A caller asks for greet("Ada"). Routing selects the deployed publication, and an activation runs the function with fresh guest state.
5. Return and clean up. The caller receives the answer; the node reclaims the activation's resources. The deployment remains available for another call.

The first-node walkthrough lets you try this sequence with an echo function. Creating a capsule adds the greeting example.

The identifiers you keep

Identifier	What it tells you	When you need it
Component checksum	Which compiled program bytes you have	Checking an artifact or diagnosing a mismatched build
Package checksum	Which complete package, including its metadata and assets, you have	Signing, transfer and package inspection
Publication ID	Which admitted publication belongs to a tenant	Selecting a program for deployment or changing its lifecycle
Deployment name	Which configured service deployment you are changing	Reading, updating or deleting a deployment
Deployment generation	Which version of that deployment you read	Preventing an update from overwriting somebody else's change
Activation ID	Which individual call you are asking about	Looking up status or requesting cancellation
Operation ID	Which managed administrative change you submitted	Recovering its retained result after a lost response

The CLI can write these values to JSON files. The tutorials read them for you; you do not need to copy long checksums by hand. A checksum or ID identifies something, but it does not grant permission to use it. Your authenticated tenant, current policy and the selected operation determine permission.

A package can change without changing its program?for example, when its software inventory is corrected. Publishing the same bytes in two tenants also creates separate publication identities. Do not substitute a component checksum where a command asks for a publication ID.

What happens when you update a service

Build and publish the changed capsule, then update the deployment to select the new publication. Supply the generation you last read so a competing change causes a conflict instead of being overwritten.

Requests already running keep their selected revision. Later requests use the new route. Restoring an earlier version is another explicit update, and that publication must still be eligible under current policy. Keeping its bytes in a cache does not restore revoked permission.

Try this in Update and restore a capsule. The deployment reference explains route generations and managed catalog state versions when you need more detailed coordination.

What a lost response means

A timeout means the caller did not receive a result in time. The node or an external provider may already have acted. Keep the original activation or operation ID and inspect that result before deciding what to do next.

Unknown means retained history cannot establish the result; the record may have expired. It does not mean the operation never happened. Uncertain means durable confirmation is unresolved. The client guide and operator reference explain the lookup methods.

Likewise, an accepted cancellation request is not proof that cleanup has finished. Active work remains accounted for until its owner has stopped it and released its resources. Deployments retain bounded metadata while idle, but they do not each keep a running guest instance.