.gitlab-ci.yml error: "apk: command not found"

Well, it turns out I had two different runners: one marked as "shell executor" (Ubuntu) and the other marked as "docker executor“.

This error was being thrown out only when the Ubuntu runner was dispatching the job, since Ubuntu doesn´t come with apk.

I disabled the Ubuntu runner and solved the problem.

The alternative is to set your installation on step above test, as in this issue

image: docker:latest

services:
- docker:dind

before_script:
- apk add --update python-pip