Install slices in a rock

In this tutorial, you will create a lean hello-world rock that uses chisel slices, and then compare the resulting rock with the one created without slices in Create a “Hello World” rock.

Prerequisites

Install Rockcraft

Install Rockcraft on your host:

snap install rockcraft --classic

Project Setup

Create a new directory, write the following into a text editor and save it as rockcraft.yaml:

name: chiselled-hello
summary: Hello world from Chisel slices
description: A "bare" rock containing the "hello" package binaries from Chisel slices.
license: Apache-2.0

version: "latest"
base: bare
build_base: "[email protected]"
platforms:
  amd64:

parts:
  hello:
    plugin: nil
    stage-packages:
      - hello_bins

Note that this Rockcraft file uses the hello_bins Chisel slice to generate an image containing only files that are strictly necessary for the hello binary. See Chisel for details on the Chisel tool.

Pack the rock with Rockcraft

To build the rock, run:

rockcraft pack

The output will look similar to:

Launching instance...
Retrieved base bare for amd64
Extracted bare:latest
Executed: pull hello
Executed: overlay hello
Executed: build hello
Executed: stage hello
Executed: prime hello
Executed parts lifecycle
Exported to OCI archive 'chiselled-hello_latest_amd64.rock'

The process might take a little while, but at the end, a new file named chiselled-hello_latest_amd64.rock will be present in the current directory. That’s your chiselled-hello rock, in oci-archive format.

Run the rock in Docker

First, import the recently created rock into Docker:

sudo /snap/rockcraft/current/bin/skopeo --insecure-policy copy oci-archive:chiselled-hello_latest_amd64.rock docker-daemon:chiselled-hello:latest

Now you can run a container from the rock:

docker run --rm chiselled-hello:latest exec hello -t

Which should print:

hello, world

The chiselled-hello image will have a size of 5.6 MB, which is much less in size than the 8.8 MB hello rock created in Create a “Hello World” rock.