reveal.js

## Debugging GitHub Actions locally

Pascal Führlich

notes:
https://rsecon2022.society-rse.org/walkthroughs/
30 min presentation, 15 min questions

### storytime
- repo on GitHub with CI
- CI = continuous integration 
- CI ~ checks run on server on each push 
- CI checks fail, locally checks succeed 
- workflow  
```python
while CI fails:
	come up with idea
	implement potential fix
	push to GitHub
	wait 20 minutes
```

notes:
- then you run out of ideas and start putting `print` statements everywhere, push again...
- this trial & error approach reminds you of the time when you just started learning to program
- nothing seemed to work and it was frustrating as hell

notes:
- at the end of your workday your history on GitHub shows 20 commits each with a red "failed" cross
- and the worst thing: you still have no idea what's going wrong
- luckily, there's a better way, and we'll take a look at that now

### Requirements
- Windows, Mac, Linux
- git
- repo on GitHub

---

## Motivation

### why CI testing?
- run checks/tests on PR/push
- prevent broken projects, especially problematic if many devs/users
- ensure setup works on fresh machine
- code quality standard

### why GitHub Actions?
- Actions are easy to setup & free
- Actions = code -> will break eventually, and then?
- debugging! 
- is quite tricky here :( 
notes:
shoutout to GitHub, amazing service for free!

### why is debugging Actions tricky?
- Action runs on a GitHub server -> non-interactive
- trial & error? upload tons of commits + print debugging?
- instead use act by Casey Lee

---

## Setup repo
- create [repo](https://github.com/pfuehrlich-pik/GitHub-Action-Example)
- add GitHub Action
- follow Action running in browser

notes:
- using R, but works with any language
- github action failed on GitHub
- ok, let's fix this locally... -> cannot reproduce!

## Setup act
- install [docker](https://www.docker.com/)
- install [act](https://github.com/nektos/act#installation)
- optional: download [GitHub Actions docker image](https://github.com/nektos/act#runners)

```sh
docker pull ghcr.io/catthehacker/ubuntu:full-latest
```

notes:
- when Action runs on GitHub server, runs in sandbox/virtual ubuntu system
- want to reproduce locally -> need same system -> docker image
- use to create container: virtual system, can have different tools/OS running there

---

## Debug Action locally
### run Action locally
```sh
act -P ubuntu-latest=ghcr.io/catthehacker/ubuntu:full-latest
```

1. creates docker container 
1. copies local files from the git repo into container 
1. runs Actions

### open bash in container

```sh
docker ps # show running containers
docker exec -it {container-name-or-id} bash
```

notes:
- compare local vs in docker: interactive R session, `source("script.R")`, `str(x)`
- difference = `factor` vs `chr` -> explicitly set `stringsAsFactors = TRUE`
- upload to GitHub
- push fix to GitHub
- open running Action in browser
- back to presentation, next slide

---

## Wrap-up
- GitHub Actions are great, trial & error debugging is terrible
- recreated server environment locally 
- ran Action locally 
- solved problem interactively 
- much faster feedback loop 
- also helpful for developing new Action!

notes:
- switch back to succeeded Action
- then next slide

## final slide
[pascal.fuehrlich@pik-potsdam.de](mailto:pascal.fuehrlich@pik-potsdam.de)

[github.com/pfuehrlich-pik](https://github.com/pfuehrlich-pik)

[pfuehrlich-pik.github.io/Debugging-GitHub-Actions-locally](https://pfuehrlich-pik.github.io/Debugging-GitHub-Actions-locally/)

[presentation created with reveal.js by Hakim El Hattab](https://revealjs.com/)

[like act? sponsor Casey Lee](https://github.com/sponsors/cplee)