While kicking the tires of Fly last week, the blog post Deploy a Sat Serverless function with to Fly.io was published. This simple wasm function written in Go makes another nice example of how to run workloads on fly.io.
But I wondered if the manual steps to build and run the container could be baked into a Dockerfile for remote builds on Fly so that wasm functions can be built from Go source and started with a single command.
Here is my first stab at just the last steps of a Dockerfile for remote builds on Fly.
‘flyctl launch --name sha18’’ just grabs the compiled sha256.wasm binary from the GitHub repo and deploys it with ‘sat’:
FROM suborbital/sat:latest
# copy wasm from local git tree
# https://github.com/wasm-builders/sat-on-fly/blob/main/sha256/sha256.wasm
COPY ./sha256.wasm .
ENV SAT_HTTP_PORT 8080
# otherwise, sat will listen on random high port, see
# Publish your Runnables on wapm.io
# https://www.wasm.builders/k33g_org/publish-your-runnables-on-wapmio-49k0
# SAT_HTTP_PORT=8080 sat https://registry-cdn.wapm.io/contents/k33g/forty-two/1.0.0/forty-two.wasm
ENTRYPOINT [ "sat", "./sha256.wasm" ]
It returns the test vector for the example shown in the Blog post:
rs@penguin:~/fly.io/wasmSHA256$ curl -d '👋 Hello World 🌍' https://sha18.fly.dev
uC-S3Jtx3j3NVm7KF8jv_Zus9zPmWCd3g_lROeLtB-Y=
As a novice to both Fly and Dockerfile, I would be happy to learn from others how to add the missing steps to the Dockerfile that compile the Go source into the wasm function, e.g. how to do this properly 
$ fly logs
2022-05-02T05:35:49Z runner[525e05fc] fra [info]Starting instance
2022-05-02T05:35:49Z runner[525e05fc] fra [info]Configuring virtual machine
2022-05-02T05:35:49Z runner[525e05fc] fra [info]Pulling container image
2022-05-02T05:35:52Z runner[525e05fc] fra [info]Unpacking image
2022-05-02T05:35:53Z runner[525e05fc] fra [info]Preparing kernel init
2022-05-02T05:35:54Z runner[525e05fc] fra [info]Configuring firecracker
2022-05-02T05:35:54Z runner[525e05fc] fra [info]Starting virtual machine
2022-05-02T05:35:54Z app[525e05fc] fra [info]Starting init (commit: 252b7bd)...
2022-05-02T05:35:54Z app[525e05fc] fra [info]Preparing to run: `sat ./sha256.wasm` as sat
2022-05-02T05:35:54Z app[525e05fc] fra [info]2022/05/02 05:35:54 listening on [fdaa:0:5f91:a7b:66:525e:5fc:2]:22 (DNS: [fdaa::3]:53)
2022-05-02T05:35:54Z app[525e05fc] fra [info]{"log_message":"(W) configured to use HTTP with no TLS","timestamp":"2022-05-02T05:35:54.995310031Z","level":2,"app":{"sat_version":"v0.1.2"}}
2022-05-02T05:35:55Z app[525e05fc] fra [info]{"log_message":"(I) starting sha256 ...","timestamp":"2022-05-02T05:35:55.016314045Z","level":3,"app":{"sat_version":"v0.1.2"}}
2022-05-02T05:35:55Z app[525e05fc] fra [info]{"log_message":"(I) serving on :8080","timestamp":"2022-05-02T05:35:55.016479725Z","level":3,"app":{"sat_version":"v0.1.2"}}
2022-05-02T05:36:07Z app[525e05fc] fra [info]{"log_message":"(I) POST /","timestamp":"2022-05-02T05:36:07.616963188Z","level":3,"app":{"sat_version":"v0.1.2"},"scope":{"request_id":"9089130d-4748-4028-b006-15164b1ee44d"}}
2022-05-02T05:36:07Z app[525e05fc] fra [info]{"log_message":"(I) POST / completed (200: OK) in 2ms","timestamp":"2022-05-02T05:36:07.618655989Z","level":3,"app":{"sat_version":"v0.1.2"},"scope":{"request_id":"9089130d-4748-4028-b006-15164b1ee44d"}}
P.S. The size of the image deployed by Fly is:
Image size: 49 MB