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Daniel Doubrovkine

aka dB., @awscloud, former CTO @artsy, +@vestris, NYC

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Migrating from Dokku to DigitalOcean Apps
mongodb | slack

In 2016 I moved half a dozen apps from Heroku to a DigitalOcean droplet to save money. I found dokku, a docker-powered PaaS. It was already quite mature, and worked flawlessly. In 2023 I am moving back from the single droplet to apps, but staying on DigitalOcean. It was a good 7-year-long run for my droplet!

What am I moving?

I’ve got 4 profitable, and 5 money-losing or free Slack apps, all open-source.

Why move?

Over the years I got increasingly nervous about doing any kind of maintenance operations on the Linux droplet. Upgrading Dokku, or its plugins, under half a dozen applications had the potential side effect of taking all my projects down at once. Before doing anything drastic, I would cautiously snapshot my droplet. For major upgrades, I would even power the droplet down before making a snapshot, incurring half an hour of downtime. Then I’d type sudo apt-get upgrade, fingers crossed. A couple of times these operations would render the host inoperable, so I’d revert and figure out a manual path forward.

In early 2022 the inevitable happened: I got permanently stuck with an old Linux distro that just would not upgrade the ancient 3.13 kernel to 4.x. Slack runs periodic pentests on its marketplace bots, and I was now running on non-LTS versions of Ruby, whereas newer versions would not work on the old kernel (securerandom.rb:75:in ‘urandom’: failed to get urandom (RuntimeError)). I was forced to upgrade, but every attempt to bring my Dokku apps back up on a 4.x kernel failed. Docker refused to start with my existing data.

I finally had to accept that I was just not smart enough to understand what “aufs is not supported anymore” meant, or how I was supposed to “use overlay” without losing all my existing data, despite the fact that “as far as people know, only ephemeral container data is stored in that aufs path”. I was that old to understand how Docker worked. I’ve finally reached the level of my incompetence!

The only workable solution was to provision a new server with a newer Linux distro, and migrate everything to it. Instead, I decided to evaluate other options. Because DigitalOcean had been a reliable and trusted platform for 7 years, I went with DigitalOcean apps.

Migration Cookbook

Here’s a migration cookbook, mostly for my own reference.

Prepare

Lower the DNS TTL to a minute about an hour prior to migration.

Migrate Data

  1. Stop the dokku container on the droplet with dokku ps:stop app.
  2. Lock the app to prevent future accidental deployments with dokku apps:lock app.
  3. Export data from MongoDB with dokku mongo:export app > app.dump.gz.
  4. Fetch the data from the droplet and back it up with scp root@domain:/path/to/data/app.dump.gz ..
  5. Restore data into the new managed MongoDB database.
mongorestore
  --uri "mongodb+srv://doadmin:password@db/admin?authSource=admin&replicaSet=db&tls=true" 
  --gzip
  --archive=app.dump.gz
  --nsInclude=app.*`.

Create an App

  1. Set the new name to app.
  2. Choose a GitHub repository for source code, grant permissions as needed.
  3. Hit Edit Plan, reduce containers to 1, choose a $5 basic or $12/pro plan.
  4. Hit Add Resource, and add a previously created MongoDB database, which adds a user with proper authorizations.
  5. Edit environment settings. Copy them from dokku config app on the droplet. Remove DATABASE_URL that was added automatically, since it doesn’t include the right database name.
  6. Set the MongoDB database URL MONGO_URL: mongodb+srv://${db.USERNAME}:${db.PASSWORD}@${db.HOSTNAME}/app?authSource=admin&replicaSet=db&tls=true.
  7. Change a default app name to app.
  8. Deploy the app.

Finish

Add a domain in app settings, update the DNS entry, re-increase back the DNS record TTL.

Cost Comparison

My monthly server total was $134.39 ($96 for a s-8vcpu-16gb droplet, $4.89 for droplet snapshots, $19.20 for droplet backups, $10.00 for an external 100GB volume for MongoDB data, and $4.30 for volume snapshots).

Monthly app cost is $103 (5x$5 for basic apps, 4x$12 for pro, $30.00 for a shared 1gb-1vcpu-15gb MongoDB).

It’s actually cheaper to use apps than the droplet for roughly the same capacity and availability, minus having to manage infrastructure.

I think DigitalOcean apps are priced very well for my use-case. If you’ve never used the platform, sign up for an account using my referral link, and thank you.