Cogini Blog
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Deploying an Elixir app to Digital Ocean with mix_deploy Port forwarding with iptables
Choosing a Linux distribution
I have been using Linux since 1993, so I will give a bit of a history lesson to explain the motivation behind the popular distributions. There are two main families, RedHat and Debian. RedHat traditionally comes from the corporate world, and Debian from the free software community. Read more…
Benchmarking Phoenix on Digital Ocean
Just for fun, I decided to benchmark the performance of the elixir deploy template running on a $5/month Digital Ocean Droplet. Read more…
SaaS pricing: users are not all the same
It's popular these days to use hosted applications instead of running your own infrastructure. It's frustrating as a customer, though, when the pricing model is not sophisticated enough to match your actual usage. In a SaaS product, your pricing should scale with the value the customer gets from the product … Read more…
Avoiding GenServer bottlenecks
GenServers are the standard way to create services in Elixir. At it's heart, a GenServer is a separate process (thread) that receives messages, does some work, manages state, and sends responses back. If that's what you want, great. It's important to recognize, though, that a GenServer only handles one request … Read more…
Database migrations in the cloud
Database migrations are used to automatically keep the database in sync with the code that uses it. Elixir apps should be deployed as releases, supervised by systemd. Here is an example of how to run migrations when deploying Elixir releases. It's tempting to automatically run database migrations when the app … Read more…
Deploying Elixir apps without sudo
We normally deploy Elixir apps as releases, supervised by systemd. After we have deployed the new release, we restart the app to make it live: sudo /bin/systemctl restart foo The user account needs sufficient permissions to restart the app, though. Instead of giving the deploy account full sudo permissions … Read more…
Getting the client public IP address in Phoenix
When your app is running behind a proxy like Nginx or a CDN, then the requests will all look like they are coming from the proxy. Use the X-Forwarded-For header to set the remote_ip correctly. Read more…
Port forwarding with iptables
In order to listen on a TCP port less than 1024, an app traditionally needs to be started as root. Over the years this has resulted in many security problems. A better solution is to run the application on a normal port such as 4000, and redirect traffic in the … Read more…
Rate limiting Nginx requests
Any popular service may be the unfortunate recipient of a DDOS attack. We find that DDOS load ends up driving capacity planning, as it can easily be 10x the normal load. You can rate limit at multiple levels. You might use a service such as CloudFlare, filtering provided by your … Read more…
Serving your Phoenix app with Nginx
It's common to run web apps behind a proxy such as Nginx or HAProxy. Nginx listens on port 80, then forwards traffic to the app on another port, e.g. 4000. Following is an example nginx.conf config: user nginx; worker_processes auto; error_log /var/log/nginx/error.log warn; pid … Read more…