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title = "SIP 005 - Application Manifest Redesign" template = "main" date = "2022-05-20T13:22:30Z"

Summary: A new design for Application Manifests (spin.toml)

Owner: lann.martin@fermyon.com

Created: May 20, 2022 Updated: Sep 11, 2023

Background

Spin's Application Manifest file (usually named spin.toml) describes a Spin application's metadata, components, and trigger configurations. The current design supports a single trigger type and combines component and trigger configuration with an implicit one-to-one relationship:

spin_manifest_version = "1"
name = "hello-world"
trigger = { type = "http", base = "/hello" }

[[component]]
id = "hello"
# ...
[component.trigger]
route = "/hello"

In order to support future features, we would like to enable more flexible trigger configurations:

  • Multiple trigger types in an application
    • an HTTP trigger that sends asynchronous jobs to a Redis trigger
  • Multiple triggers associated with a single component
    • a file server component serving multiple HTTP trigger routes
  • One trigger associated with multiple components
    • an HTTP trigger with middleware components

Proposal

Manifest version

Since this proposal represents a backward-incompatible change to the manifest format, the manifest version changes.

Note that this also changes the version from a string to an int, which is a minor/optional change for this proposal.

spin_manifest_version = 2

Global trigger config

In order to allow for multiple trigger types, we remove the top-level trigger.type field. We also move all application metadata from the top-level config to a new [application] section, and all "global trigger config" to new [application.trigger.<type>] sections:

[application]
name = "hello-world"
[application.trigger.http]
base = "/hello"

In the short term we can continue to enforce the use of exactly one trigger type in an application as a manifest validation step.

Component config

Component IDs will become more important under this design, which we can emphasize by moving the ID into the section header (aka TOML table key):

[component.hello-world]
# instead of id = "hello-world"

Trigger config

In order to decouple triggers and components, we move triggers to new top-level [[trigger.<type>]] sections:

[[trigger.http]]
route = "/hello"
handler = "hello"
[component.hello]
# ...

Component inline config

In addition to being defined in their own top-level sections and referenced by ID, component configs may be inlined; allowing this:

[[trigger.http]]
route = "/hello"
handler = { source = "hello.wasm" }

which would be equivalent to:

[[trigger.http]]
route = "/hello"
handler = "<generated-id>"
[component.<generated-id>]
source = "hello.wasm"

Rename config

The Spin config feature is easily confused with Spin "Runtime Config". We can adopt the variables terminology which is already used by the top-level [variables] section and rename [component.config] to [component.variables].

Backward compatibility

Existing "version 1" manifests can be transformed into this "version 2" format losslessly:

trigger = { type = "http", base = "/" }
[[component]]
id = "hello"
source = "hello.wasm"
[component.trigger]
route = "/hello"

is equivalent to:

[application.trigger.http]
base = "/"
[[trigger.http]]
route = "/hello"
handler = "hello"
[component.hello]
source = "hello.wasm"

This upgrade could be performed automatically by spin doctor.

Design options

Remove http base

This trigger option is rarely used and has caused implementation headaches. For any (rare) existing applications that do use it, the spin doctor upgrade path could inline the base into the trigger route(s).