5-update-&-rollback.md

Update & Rollback

This tutorial covers:

1. Making a change to a system and deploying it.
2. Rolling a deployed system back to a known good state
3. Rolling a deployed system forward after applying a full fix

Before Making any Changes

cd into the sudc/workspace/sudc-web directory and run a git branch command. If the HEAD is detached, then do

git checkout master

The HEAD may already have been detached depending on how you've followed the workshops. (more on that later)

Add a buggy alert

Let's break something! Open up sudc/workspace/sudc-web/web/public/js/app.js and add an alert after the 'Your code here' comment:

initialize: function () {
    // Your code here
    alert('whoops');
}

cd into the sudc/workspace/sudc-web directory, stage the changes and commit:

git add .
git commit -m "Added buggy alert"

Build the container and deploy the latest revision:

nscale system compile sudc development
nscale container build sudc web latest development
nscale revision deploy sudc latest development

Check the site for the buggy alert:

OS X: open http://$(boot2docker ip):8000

Linux: open localhost:8000

It is this workflow which allows us to makes changes and deploy them using nscale:

- Make changes in code
- Commit
- (optional) push to Github
- System compile
- Build relevant container(s)
- System Deploy

Pay particular attention to the fact that when building containers nscale, will checkout repos using the sha of the latest commit. This will detach the HEAD your repos. The danger is that you build containers which detaches the HEAD, edit code on an unreferenced branch, and then do a system compile which checks out the master branch in each repo. You could potentially lose work.

Tip: Before writing code that you are building into a container, do a git status of that repo to make sure the HEAD isn't detached or else you will be writing code on an unnamed branch. Checkout to master or another branch before proceeding.

Roll back

It's time to quickly rollback, picking the second revision id:

nscale revision list sudc
nscale revision deploy sudc <revision id> development

Check the site is working:

OS X: open http://$(boot2docker ip):8000

Linux: open localhost:8000

Roll forward

The site is back up and running so let's fix the bug in the code and apply that fix. remove the alert statement from app.js and commit the change or:

open the sudc/workspace/sudc-web directory

git checkout master (because the HEAD is now detached from the container being built)
git revert HEAD --no-edit

Roll forward the change:

nscale system compile sudc development
nscale container build sudc web latest development
nscale revision deploy sudc latest development

Check the site is working:

OS X: open http://$(boot2docker ip):8000

Linux: open localhost:8000

Next up: exercise 6