Image Configuration

The container configuration (application/vnd.wasm.config.v0+json) defines how the container should be run. It is a collection of metadata that controls the container’s runtime behavior, including environment variables, execution parameters, hardware permissions, and entry points.

For Ocre containers, this configuration is specifically tailored to WebAssembly modules running in embedded environments, ensuring proper initialization and execution within resource constraints.

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Configuration Structure

The configuration file follows the OCI Image Manifest specification with modifications for Wasm and embedded environments. See the example and a detailed description of its elements below.

Example

{
  "architecture": "wasm",
  "os": "wasip1",
  "layerDigests": [
    "sha256:71cb138990af165c4baf0c43361e5c055ed60a5d2632ee547597be56dcfa07e2"
  ],
  "module": {
    "entryPoint": "on_init"
  }
}

Configuration Elements

Elements within the configuration are defined as follows:

Element	Type	Required	Description
architecture	string	Yes	CPU architecture of the binaries in this image; this value MUST be set to wasm
os	string	Yes	Operating system which this image is built to run on; this MUST be wasip1 or wasip2 according to the Wasm target type
layerDigests	array	Yes	Digests of all of the layers this configuration targets; digests must be in the same order as in the image manifest file
module	module object	Yes	Specifies the parameters used for execution; entryPoint defines the WASM function to call on container start

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Future Enhancements

Ocre will extend its configuration format to better align with OCI standards and support critical runtime elements through the config entry. This enhancement will enable control over environment variables, permissions, and additional runtime parameters that are essential for container operation.

Here’s an example of how these configurations will be structured:

{
  "config": {
    "Env": [
      "name1=val1",
      "name2=val2"
    ],
    "Permissions": [
      "perm1",
      "perm2"
    ]
  }
}