https://github.com/cynicdog/elixir-in-container
Cloud-native Elixir templates 🧑🏻💻
https://github.com/cynicdog/elixir-in-container
docker elixir
Last synced: 2 months ago
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Cloud-native Elixir templates 🧑🏻💻
- Host: GitHub
- URL: https://github.com/cynicdog/elixir-in-container
- Owner: CynicDog
- Created: 2025-06-29T10:55:00.000Z (12 months ago)
- Default Branch: main
- Last Pushed: 2025-07-08T12:36:59.000Z (12 months ago)
- Last Synced: 2026-03-29T07:37:30.713Z (3 months ago)
- Topics: docker, elixir
- Language: Elixir
- Homepage:
- Size: 40 KB
- Stars: 0
- Watchers: 0
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Elixir in Container ☁️
## Hello World!
> This section demonstrates how to run an Elixir app inside a Docker container and interact with it via HTTP and distributed BEAM nodes.
#### Pull image from this repository package
```bash
cynocdig@CynicDogs-MacBook % docker pull ghcr.io/cynicdog/containerized_elixir:latest
```
#### Run Docker container with port 8080 exposed
```bash
cynocdig@CynicDogs-MacBook % docker run -p 8080:8080 --rm -d ghcr.io/cynicdog/containerized_elixir:latest
```
#### httpie to the container..
```bash
cynocdig@CynicDogs-MacBook % http :8080/greet
HTTP/1.1 200 OK
cache-control: max-age=0, private, must-revalidate
content-length: 59
content-type: text/plain; charset=utf-8
date: Tue, 08 Jul 2025 12:26:48 GMT
server: Cowboy
🚀 Elixir inside a container — greetings from the BEAM!
```
## Communicate with an Elixir Node in Docker Container
> This guide shows how to set up distributed Elixir nodes between your **host machine (macOS)** and a **Docker container** using node names and cookies, and how to call functions remotely.
### On Host Machine 🧑🏻💻
##### Start a BEAM node on the host machine
```bash
cynocdig@CynicDogs-MacBook % iex --name host@host.docker.internal --cookie mycookie
````
### On Docker Container 🐋
##### Run the container with network configuration
```bash
cynocdig@CynicDogs-MacBook % docker run -it --rm \
--add-host host.docker.internal:host-gateway \
elixir bash
```
##### Curious about `host.docker.internal`?
If you check the container’s `/etc/hosts` file, you’ll see something like:
```bash
root@container:/# cat /etc/hosts
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
...
192.168.65.254 host.docker.internal
```
> That `192.168.65.254 host.docker.internal` line is a special DNS entry Docker provides to containers to reach the host machine.
##### Start a BEAM node inside the container
```bash
root@3e185f96415a:/# iex --name elixir_node@container --cookie mycookie
```
##### Connect container node to host node
```bash
iex(elixir_node@container)1> Node.connect(:'host@host.docker.internal')
```
### Say Hello to the Host Node!
Define a module on both the host node:
```elixir
defmodule Greet do
def say_hello do
IO.puts("Hello 👋🏻 from #{node()}! 🐋")
end
end
```
> Avoid sending anonymous functions between remote nodes. Distributed BEAM nodes send function “closures” as a serialized object. For remote execution (e.g., `Node.spawn/2`), the function must be sent (serialized) over the network.
Then, from the container node IEx shell, call the function remotely on the host node:
```bash
iex(elixir_node@container)2> Node.spawn(:"host@host.docker.internal", Greet, :say_hello, [])
```
## Inspecting and Using `epmd` in a Container
> This section explores how to inspect and interact with the **Erlang Port Mapper Daemon (epmd)** inside a running Elixir Docker container. This is useful for understanding how distributed Elixir nodes discover each other via `epmd`.
#### Start an Elixir Container
```bash
ginsenglee@Ginsengs-MacBook-Air ~ % docker run -it --name nostalgic_banzai \
--add-host host.docker.internal:host-gateway \
elixir bash
```
#### Locate the `epmd` Binary
```bash
root@e9e6d65de9af:/# which epmd
/usr/local/bin/epmd
```
#### Manually Start `epmd`
```
root@e9e6d65de9af:/# epmd -daemon
root@e9e6d65de9af:/# ps aux | grep epmd
root 19 0.0 0.0 2824 928 ? S 06:46 0:00 epmd -daemon
```
#### Look Up Listening Ports
```
root@e9e6d65de9af:/# netstat -tlnp | grep 4369
tcp 0 0 0.0.0.0:4369 0.0.0.0:* LISTEN 19/epmd
tcp6 0 0 :::4369 :::* LISTEN 19/epmd
```
> This requires `net-tools` installed on the container. If not installed, run the command of `apt-get update && apt-get install net-tools ` to download the binary.
#### Check for Registered Nodes
Initially there will be no nodes:
```
root@e9e6d65de9af:/# epmd -names
epmd: up and running on port 4369 with data:
```
#### Open a Second Terminal in the Same Container
```
ginsenglee@Ginsengs-MacBook-Air ~ % docker exec -it nostalgic_banzai bash
```
Start a named Elixir node:
```
root@e9e6d65de9af:/# iex --name node_in_container_1@container --cookie my_cookie
```
You should now see this node registered with `epmd` in the first container:
```bash
root@e9e6d65de9af:/# epmd -names
epmd: up and running on port 4369 with data:
name node_in_container_1 at port 33911
```