Spin App OCI Diagnostics

spin-app-oci-diagnostics.md

Spin App as OCI image diagnostics

Publish and pull app

Navigate to app directory and perform a roundtrip push/pull of the app to/from a registry (here using ttl.sh):

export IMAGE_NAME=$(uuidgen | tr '[:upper:]' '[:lower:]')
spin registry push ttl.sh/${IMAGE_NAME}:1h
spin registry pull ttl.sh/${IMAGE_NAME}:1h

Navigate to registry cache

Navigate to Spin's registry cache at $XDG_CACHE_HOME. On Mac, this is ~/Library/Caches/spin/registry

cd ~/Library/Caches/spin/registry

High-level layout can be seen.

$ tree -L 1
.
├── data
├── manifests
└── wasm

4 directories, 0 files

• data holds data (eg static asset) layers
• manifests holds OCI manifest (manifest.json) and Spin's locked app config (config.json) under image reference path
• wasm holds wasm component layers

We're interested in the manifests under the sub-dir for our app in manifests, eg:

$ ls -l manifests/ttl.sh/bc445bdd-e571-4966-ad25-280d83b178b4/1h
total 24
-rw-r--r-- 1 vdice staff 10880 Mar 13 16:08 config.json
-rw-r--r-- 1 vdice staff 10270 Mar 13 16:08 manifest.json

config.json

The locked app config that Spin builds (config.json) contains Spin app metadata, trigger config, component listing along with the list of layers included with each, etc.

We can get a view into precisely which layers/assets are bundled in each component via:

cat manifests/ttl.sh/bc445bdd-e571-4966-ad25-280d83b178b4/1h/config.json | jq -r '.components'

manifest.json

The OCI manifest (manifest.json) contains a listing of all the layers, their types and their sizes:

$ cat manifests/ttl.sh/bc445bdd-e571-4966-ad25-280d83b178b4/1h/manifest.json | jq -r '.'
{
  "schemaVersion": 2,
  "config": {
    "mediaType": "application/vnd.oci.image.config.v1+json",
    "digest": "sha256:1c27590edc5daec38a8d418b95c56ad501dd7ce80a11bfbaab79fe3dfe5264aa",
    "size": 209
  },
  "layers": [
    {
      "mediaType": "application/vnd.wasm.content.layer.v1+wasm",
      "digest": "sha256:26211586b5373cbacc116be3f5c7b7d029894d7e27cf6c20cdd2a65e8b03a24c",
      "size": 3770121
    },
...

If we'd like to tally up the total size of all layers for this app/OCI image, we can use this one-liner that is sure to impress (or frighten)!

$ total=''; for size in $(cat manifests/ttl.sh/bc445bdd-e571-4966-ad25-280d83b178b4/1h/manifest.json | jq -r '.layers' | grep size | cut -d ':' -f 2 | tr -d " "); do total=`expr $total + $size`; done; echo $total
72428333