Day 23: Terraform - Writing and applying configuration files
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Terraform configuration files are usually written in HCL (HashiCorp Configuration Language), though JSON works too. HCL is recommended: all the documentation uses it, and it reads more easily than JSON. The file extension is *.tf.
A configuration file typically holds resource definitions, variable definitions, data sources, and other infrastructure components. Here is an example main.tf that runs an nginx Docker container (taken from the official docs):
terraform {
required_providers {
docker = {
source = "kreuzwerker/docker"
version = "~> 3.0.1"
}
}
}
provider "docker" {}
resource "docker_image" "nginx" {
name = "nginx"
keep_locally = false
}
resource "docker_container" "nginx" {
image = docker_image.nginx.image_id
name = "tutorial-debakarr"
ports {
internal = 80
external = 8000
}
}The commands you will use most often:
terraform init— initializes the working directory, downloading required providers and setting up the backend.terraform validate— checks the configuration files for syntax errors and other issues.terraform plan— builds an execution plan showing what Terraform will do to reach the desired state.terraform apply— executes the plan and changes the infrastructure accordingly.terraform destroy— deletes the infrastructure Terraform manages.
What each command does against the main.tf above:
terraform initsets up the working directory and installs the Docker provider (kreuzwerker/docker).terraform validateconfirms the configuration is syntactically valid and processable.terraform plancompares current state with desired state and reports that a Docker image and container will be created.terraform applydownloads thenginximage, creates the container, and maps container port 80 to host port 8000.terraform destroyremoves the container and image — useful for cleanup or starting fresh.
Here is the full session from my machine:
debakarr@debakarr-mobl MINGW64 /c/Source/tf-demo/docker
$ terraform init
Initializing the backend...
Initializing provider plugins...
- Reusing previous version of kreuzwerker/docker from the dependency lock file
- Using previously-installed kreuzwerker/docker v3.0.2
Terraform has been successfully initialized!
You may now begin working with Terraform. Try running "terraform plan" to see
any changes that are required for your infrastructure. All Terraform commands
should now work.
If you ever set or change modules or backend configuration for Terraform,
rerun this command to reinitialize your working directory. If you forget, other
commands will detect it and remind you to do so if necessary.
debakarr@debakarr-mobl MINGW64 /c/Source/tf-demo/docker
$ terraform validate
Success! The configuration is valid.
debakarr@debakarr-mobl MINGW64 /c/Source/tf-demo/docker
$ terraform plan
Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
+ create
Terraform will perform the following actions:
# docker_container.nginx will be created
+ resource "docker_container" "nginx" {
+ attach = false
+ bridge = (known after apply)
+ command = (known after apply)
+ container_logs = (known after apply)
+ container_read_refresh_timeout_milliseconds = 15000
+ entrypoint = (known after apply)
+ env = (known after apply)
+ exit_code = (known after apply)
+ hostname = (known after apply)
+ id = (known after apply)
+ image = (known after apply)
+ init = (known after apply)
+ ipc_mode = (known after apply)
+ log_driver = (known after apply)
+ logs = false
+ must_run = true
+ name = "tutorial-debakarr"
+ network_data = (known after apply)
+ read_only = false
+ remove_volumes = true
+ restart = "no"
+ rm = false
+ runtime = (known after apply)
+ security_opts = (known after apply)
+ shm_size = (known after apply)
+ start = true
+ stdin_open = false
+ stop_signal = (known after apply)
+ stop_timeout = (known after apply)
+ tty = false
+ wait = false
+ wait_timeout = 60
+ ports {
+ external = 8000
+ internal = 80
+ ip = "0.0.0.0"
+ protocol = "tcp"
}
}
# docker_image.nginx will be created
+ resource "docker_image" "nginx" {
+ id = (known after apply)
+ image_id = (known after apply)
+ keep_locally = false
+ name = "nginx"
+ repo_digest = (known after apply)
}
Plan: 2 to add, 0 to change, 0 to destroy.
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Note: You didn't use the -out option to save this plan, so Terraform can't guarantee to take exactly these actions if you run "terraform apply" now.
debakarr@debakarr-mobl MINGW64 /c/Source/tf-demo/docker
$ terraform apply
Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
+ create
Terraform will perform the following actions:
# docker_container.nginx will be created
+ resource "docker_container" "nginx" {
+ attach = false
+ bridge = (known after apply)
+ command = (known after apply)
+ container_logs = (known after apply)
+ container_read_refresh_timeout_milliseconds = 15000
+ entrypoint = (known after apply)
+ env = (known after apply)
+ exit_code = (known after apply)
+ hostname = (known after apply)
+ id = (known after apply)
+ image = (known after apply)
+ init = (known after apply)
+ ipc_mode = (known after apply)
+ log_driver = (known after apply)
+ logs = false
+ must_run = true
+ name = "tutorial-debakarr"
+ network_data = (known after apply)
+ read_only = false
+ remove_volumes = true
+ restart = "no"
+ rm = false
+ runtime = (known after apply)
+ security_opts = (known after apply)
+ shm_size = (known after apply)
+ start = true
+ stdin_open = false
+ stop_signal = (known after apply)
+ stop_timeout = (known after apply)
+ tty = false
+ wait = false
+ wait_timeout = 60
+ ports {
+ external = 8000
+ internal = 80
+ ip = "0.0.0.0"
+ protocol = "tcp"
}
}
# docker_image.nginx will be created
+ resource "docker_image" "nginx" {
+ id = (known after apply)
+ image_id = (known after apply)
+ keep_locally = false
+ name = "nginx"
+ repo_digest = (known after apply)
}
Plan: 2 to add, 0 to change, 0 to destroy.
Do you want to perform these actions?
Terraform will perform the actions described above.
Only 'yes' will be accepted to approve.
Enter a value: yes
docker_image.nginx: Creating...
docker_image.nginx: Still creating... [10s elapsed]
docker_image.nginx: Creation complete after 15s [id=sha256:f9c14fe76d502861ba0939bc3189e642c02e257f06f4c0214b1f8ca329326cdanginx]
docker_container.nginx: Creating...
docker_container.nginx: Creation complete after 1s [id=cc21cf92096bfacf02419d197ab96be41d131e3c568bba1457800c598e80e914]
Apply complete! Resources: 2 added, 0 changed, 0 destroyed.
debakarr@debakarr-mobl MINGW64 /c/Source/tf-demo/docker
$ terraform destroy
docker_image.nginx: Refreshing state... [id=sha256:f9c14fe76d502861ba0939bc3189e642c02e257f06f4c0214b1f8ca329326cdanginx]
docker_container.nginx: Refreshing state... [id=cc21cf92096bfacf02419d197ab96be41d131e3c568bba1457800c598e80e914]
Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
- destroy
Terraform will perform the following actions:
# docker_container.nginx will be destroyed
- resource "docker_container" "nginx" {
- attach = false -> null
- command = [
- "nginx",
- "-g",
- "daemon off;",
] -> null
- container_read_refresh_timeout_milliseconds = 15000 -> null
- cpu_shares = 0 -> null
- dns = [] -> null
- dns_opts = [] -> null
- dns_search = [] -> null
- entrypoint = [
- "/docker-entrypoint.sh",
] -> null
- env = [] -> null
- group_add = [] -> null
- hostname = "cc21cf92096b" -> null
- id = "cc21cf92096bfacf02419d197ab96be41d131e3c568bba1457800c598e80e914" -> null
- image = "sha256:f9c14fe76d502861ba0939bc3189e642c02e257f06f4c0214b1f8ca329326cda" -> null
- init = false -> null
- ipc_mode = "private" -> null
- log_driver = "json-file" -> null
- log_opts = {} -> null
- logs = false -> null
- max_retry_count = 0 -> null
- memory = 0 -> null
- memory_swap = 0 -> null
- must_run = true -> null
- name = "tutorial-debakarr" -> null
- network_data = [
- {
- gateway = "172.17.0.1"
- global_ipv6_address = ""
- global_ipv6_prefix_length = 0
- ip_address = "172.17.0.3"
- ip_prefix_length = 16
- ipv6_gateway = ""
- mac_address = "02:42:ac:11:00:03"
- network_name = "bridge"
},
] -> null
- network_mode = "default" -> null
- privileged = false -> null
- publish_all_ports = false -> null
- read_only = false -> null
- remove_volumes = true -> null
- restart = "no" -> null
- rm = false -> null
- runtime = "runc" -> null
- security_opts = [] -> null
- shm_size = 64 -> null
- start = true -> null
- stdin_open = false -> null
- stop_signal = "SIGQUIT" -> null
- stop_timeout = 0 -> null
- storage_opts = {} -> null
- sysctls = {} -> null
- tmpfs = {} -> null
- tty = false -> null
- wait = false -> null
- wait_timeout = 60 -> null
- ports {
- external = 8000 -> null
- internal = 80 -> null
- ip = "0.0.0.0" -> null
- protocol = "tcp" -> null
}
}
# docker_image.nginx will be destroyed
- resource "docker_image" "nginx" {
- id = "sha256:f9c14fe76d502861ba0939bc3189e642c02e257f06f4c0214b1f8ca329326cdanginx" -> null
- image_id = "sha256:f9c14fe76d502861ba0939bc3189e642c02e257f06f4c0214b1f8ca329326cda" -> null
- keep_locally = false -> null
- name = "nginx" -> null
- repo_digest = "nginx@sha256:af296b188c7b7df99ba960ca614439c99cb7cf252ed7bbc23e90cfda59092305" -> null
}
Plan: 0 to add, 0 to change, 2 to destroy.
Do you really want to destroy all resources?
Terraform will destroy all your managed infrastructure, as shown above.
There is no undo. Only 'yes' will be accepted to confirm.
Enter a value: yes
docker_container.nginx: Destroying... [id=cc21cf92096bfacf02419d197ab96be41d131e3c568bba1457800c598e80e914]
docker_container.nginx: Destruction complete after 0s
docker_image.nginx: Destroying... [id=sha256:f9c14fe76d502861ba0939bc3189e642c02e257f06f4c0214b1f8ca329326cdanginx]
docker_image.nginx: Destruction complete after 1s
Destroy complete! Resources: 2 destroyed.