Write a Template from Scratch
This guided tour introduces you to the different parts of a Coder template by showing you how to create a template from scratch.
You'll write a simple template that provisions a workspace as a Docker container with Ubuntu.
Before you start
To follow this guide, you'll need:
When setting up your computer or computing instance, make sure to install Docker first, then Coder. Otherwise, you'll need to add the
coder
user to thedocker
group.
-
The URL for your Coder instance. If you're running Coder locally, the default URL is http://127.0.0.1:3000.
-
A text editor. For this tour, we use GNU nano.
Haven't written Terraform before? Check out Hashicorp's Getting Started Guides.
What's in a template
The main part of a Coder template is a Terraform tf
file. A Coder template often has other files to configure the other resources
that the template needs. In this tour you'll also create a Dockerfile
.
Coder can provision all Terraform modules, resources, and properties. The Coder
server essentially runs a terraform apply
every time a workspace is created,
started, or stopped.
Here's a simplified diagram that shows the main parts of the template we'll create.
1. Create template files
On your local computer, create a directory for your template and create the
Dockerfile
.
mkdir template-tour
cd template-tour
mkdir build
nano build/Dockerfile
You'll enter a simple Dockerfile
that starts with the
official Ubuntu image. In the editor, enter
and save the following text in Dockerfile
then exit the editor:
FROM ubuntu
RUN apt-get update \
&& apt-get install -y \
sudo \
curl \
&& rm -rf /var/lib/apt/lists/*
ARG USER=coder
RUN useradd --groups sudo --no-create-home --shell /bin/bash ${USER} \
&& echo "${USER} ALL=(ALL) NOPASSWD:ALL" >/etc/sudoers.d/${USER} \
&& chmod 0440 /etc/sudoers.d/${USER}
USER ${USER}
WORKDIR /home/${USER}
Notice how Dockerfile
adds a few things to the parent ubuntu
image, which
your template needs later:
- It installs the
sudo
andcurl
packages. - It adds a
coder
user, including a home directory.
2. Set up template providers
Now you can edit the Terraform file, which provisions the workspace's resources.
nano main.tf
We'll start by setting up our providers. At a minimum, we need the coder
provider. For this template, we also need the docker
provider:
terraform {
required_providers {
coder = {
source = "coder/coder"
version = "~> 0.8.3"
}
docker = {
source = "kreuzwerker/docker"
version = "~> 3.0.1"
}
}
}
provider "coder" {
}
provider "docker" {
}
locals {
username = data.coder_workspace.me.owner
}
data "coder_provisioner" "me" {
}
data "coder_workspace" "me" {
}
Notice that the provider
blocks for coder
and docker
are empty. In a more
practical template, you would add arguments to these blocks to configure the
providers, if needed.
The
coder_workspace
data source provides details about the state of a workspace, such as its name,
owner, and so on. The data source also lets us know when a workspace is being
started or stopped. We'll take advantage of this information in later steps to
do these things:
- Set some environment variables based on the workspace owner.
- Manage ephemeral and persistent storage.
3. coder_agent
All templates need to create and run a
Coder agent.
This lets developers connect to their workspaces. The coder_agent
resource
runs inside the compute aspect of your workspace, typically a VM or container.
In our case, it will run in Docker.
You do not need to have any open ports on the compute aspect, but the agent
needs curl
access to the Coder server. Remember that we installed curl
in
Dockerfile
, earlier.
This snippet creates the agent:
resource "coder_agent" "main" {
arch = data.coder_provisioner.me.arch
os = "linux"
startup_script_timeout = 180
startup_script = <<-EOT
set -e
# install and start code-server
curl -fsSL https://code-server.dev/install.sh | sh -s -- --method=standalone --prefix=/tmp/code-server --version 4.11.0
/tmp/code-server/bin/code-server --auth none --port 13337 >/tmp/code-server.log 2>&1 &
EOT
env = {
GIT_AUTHOR_NAME = "${data.coder_workspace.me.owner}"
GIT_COMMITTER_NAME = "${data.coder_workspace.me.owner}"
GIT_AUTHOR_EMAIL = "${data.coder_workspace.me.owner_email}"
GIT_COMMITTER_EMAIL = "${data.coder_workspace.me.owner_email}"
}
metadata {
display_name = "CPU Usage"
key = "0_cpu_usage"
script = "coder stat cpu"
interval = 10
timeout = 1
}
metadata {
display_name = "RAM Usage"
key = "1_ram_usage"
script = "coder stat mem"
interval = 10
timeout = 1
}
}
Because Docker is running locally in the Coder server, there is no need to
authenticate coder_agent
. But if your coder_agent
were running on a remote
host, your template would need
authentication credentials.
This template's agent also runs a startup script, sets environment variables, and provides metadata.
The
startup script
installs code-server, a browser-based
VS Code app that runs in the workspace. We'll
give users access to code-server through coder_app
, later.
The
env
block sets environments variables for the workspace. We use the data source from
coder_workspace
to set the environment variables based on the workspace's
owner. This way, the owner can make git commits immediately without any manual
configuration.
Your template can use metadata to show information to the workspace owner. Coder
displays this metadata in the Coder dashboard. Our template has
metadata
blocks
for CPU and RAM usage.
4. coder_app
A
coder_app
resource lets a developer use an app from the workspace's Coder dashboard.
This is commonly used for web IDEs such as code-server, RStudio, and JupyterLab.
To install and code-server in the workspace, remember that we installed it in
the startup_script
argument in coder_agent
. We make it available from a
workspace with a coder_app
resource. See
web IDEs for more examples.
resource "coder_app" "code-server" {
agent_id = coder_agent.main.id
slug = "code-server"
display_name = "code-server"
url = "http://localhost:13337/?folder=/home/${local.username}"
icon = "/icon/code.svg"
subdomain = false
share = "owner"
healthcheck {
url = "http://localhost:13337/healthz"
interval = 5
threshold = 6
}
}
You can also use a coder_app
resource to link to external apps, such as links
to wikis or cloud consoles.
resource "coder_app" "coder-server-doc" {
agent_id = coder_agent.main.id
icon = "/emojis/1f4dd.png"
slug = "getting-started"
url = "https://coder.com/docs/code-server"
external = true
}
5. Persistent and ephemeral resources
Managing the lifecycle of template resources is important. We want to make sure that workspaces use computing, storage, and other services efficiently.
We want our workspace's home directory to persist after the workspace is stopped so that a developer can continue their work when they start the workspace again.
We do this in 2 parts:
- Our
docker_volume
resource uses thelifecycle
block with theignore_changes = all
argument to prevent accidental deletions. - To prevent Terraform from destroying persistent Docker volumes in case of a
workspace name change, we use an immutable parameter, like
data.coder_workspace.me.id
.
You'll see later that we make sure that our Docker container is ephemeral with the Terraform count meta-argument.
resource "docker_volume" "home_volume" {
name = "coder-${data.coder_workspace.me.id}-home"
# Protect the volume from being deleted due to changes in attributes.
lifecycle {
ignore_changes = all
}
}
For details, see Resource persistence.
6. Set up the Docker container
To set up our Docker container, our template has a docker_image
resource that
uses build/Dockerfile
, which we created earlier.
resource "docker_image" "main" {
name = "coder-${data.coder_workspace.me.id}"
build {
context = "./build"
build_args = {
USER = local.username
}
}
triggers = {
dir_sha1 = sha1(join("", [for f in fileset(path.module, "build/*") : filesha1(f)]))
}
}
Our docker_container
resource uses coder_workspace
start_count
to start
and stop the Docker container:
resource "docker_container" "workspace" {
count = data.coder_workspace.me.start_count
image = docker_image.main.name
# Uses lower() to avoid Docker restriction on container names.
name = "coder-${data.coder_workspace.me.owner}-${lower(data.coder_workspace.me.name)}"
# Hostname makes the shell more user friendly: coder@my-workspace:~$
hostname = data.coder_workspace.me.name
# Use the docker gateway if the access URL is 127.0.0.1
entrypoint = ["sh", "-c", replace(coder_agent.main.init_script, "/localhost|127\\.0\\.0\\.1/", "host.docker.internal")]
env = [
"CODER_AGENT_TOKEN=${coder_agent.main.token}",
]
host {
host = "host.docker.internal"
ip = "host-gateway"
}
volumes {
container_path = "/home/${local.username}"
volume_name = docker_volume.home_volume.name
read_only = false
}
}
7. Create the template in Coder
Save main.tf
and exit the editor.
Now that we've created the files for our template, we can add them to our Coder deployment.
We can do this with the Coder CLI or the Coder dashboard. For this tour, we'll use the Coder CLI.
First, you'll need to log in to your Coder deployment from the CLI. This is where you need the URL for your deployment:
$ coder login https://coder.example.com
Your browser has been opened to visit:
https://coder.example.com/cli-auth
> Paste your token here:
In your web browser, enter your credentials:
Copy the session token into the clipboard:
And paste it into the CLI:
> Welcome to Coder, marc! You're authenticated.
$
Now you can add your template files to your Coder deployment:
$ pwd
/home/marc/template-tour
$ coder templates create
> Upload "."? (yes/no) yes
The Coder CLI tool gives progress information then prompts you to confirm:
> Confirm create? (yes/no) yes
The template-tour template has been created! Developers can provision a workspace with this template using:
coder create --template="template-tour" [workspace name]
In your web browser, log in to your Coder dashboard, select Templates. Your template is ready to use for new workspaces.