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| 1 | +# Template Dependencies |
| 2 | + |
| 3 | +When creating Coder templates, it is unlikely that you will just be using |
| 4 | +built-in providers. Part of Terraform's flexibility stems from its rich plugin |
| 5 | +ecosystem, and it makes sense to take advantage of this. |
| 6 | + |
| 7 | +That having been said, here are some recommendations to follow, based on the |
| 8 | +[Terraform documentation](https://developer.hashicorp.com/terraform/tutorials/configuration-language/provider-versioning). |
| 9 | + |
| 10 | +Following these recommendations will: |
| 11 | + |
| 12 | +- **Prevent unexpected changes:** Your templates will use the same versions of |
| 13 | + Terraform providers each build. This will prevent issues related to changes in |
| 14 | + providers. |
| 15 | +- **Improve build performance:** Coder caches provider versions on each build. |
| 16 | + If the same provider version can be re-used on subsequent builds, Coder will |
| 17 | + simply re-use the cached version if it is available. |
| 18 | +- **Improve build reliability:** As some providers are hundreds of megabytes in |
| 19 | + size, interruptions in connectivity to the Terraform registry during a |
| 20 | + workspace build can result in a failed build. If Coder is able to re-use a |
| 21 | + cached provider version, the likelihood of this is greatly reduced. |
| 22 | + |
| 23 | +## Lock your provider and module versions |
| 24 | + |
| 25 | +If you add a Terraform provider to `required_providers` without specifying a |
| 26 | +version requirement, Terraform will always fetch the latest version on each |
| 27 | +invocation: |
| 28 | + |
| 29 | +```terraform |
| 30 | +terraform { |
| 31 | + required_providers { |
| 32 | + coder = { |
| 33 | + source = "coder/coder" |
| 34 | + } |
| 35 | + frobnicate = { |
| 36 | + source = "acme/frobnicate" |
| 37 | + } |
| 38 | + } |
| 39 | +} |
| 40 | +``` |
| 41 | + |
| 42 | +Any new releases of the `coder` or `frobnicate` providers will be picked up upon |
| 43 | +the next time a workspace is built using this template. This may include |
| 44 | +breaking changes. |
| 45 | + |
| 46 | +To prevent this, add a |
| 47 | +[version constraint](https://developer.hashicorp.com/terraform/language/expressions/version-constraints) |
| 48 | +to each provider in the `required_providers` block: |
| 49 | + |
| 50 | +```terraform |
| 51 | +terraform { |
| 52 | + required_providers { |
| 53 | + coder = { |
| 54 | + source = "coder/coder" |
| 55 | + version = ">= 0.2, < 0.3" |
| 56 | + } |
| 57 | + frobnicate = { |
| 58 | + source = "acme/frobnicate" |
| 59 | + version = "~> 1.0.0" |
| 60 | + } |
| 61 | + } |
| 62 | +} |
| 63 | +``` |
| 64 | + |
| 65 | +In the above example, the `coder/coder` provider will be limited to all versions |
| 66 | +above or equal to `0.2.0` and below `0.3.0`, while the `acme/frobnicate` |
| 67 | +provider will be limited to all versions matching `1.0.x`. |
| 68 | + |
| 69 | +The above also applies to Terraform modules. In the below example, the module |
| 70 | +`razzledazzle` is locked to version `1.2.3`. |
| 71 | + |
| 72 | +```terraform |
| 73 | +module "razzledazzle" { |
| 74 | + source = "registry.example.com/modules/razzle/dazzle" |
| 75 | + version = "1.2.3" |
| 76 | + foo = "bar" |
| 77 | +} |
| 78 | +``` |
| 79 | + |
| 80 | +## Use a Dependency Lock File |
| 81 | + |
| 82 | +Terraform allows creating a |
| 83 | +[dependency lock file](https://developer.hashicorp.com/terraform/language/files/dependency-lock) |
| 84 | +to track which provider versions were selected previously. This allows you to |
| 85 | +ensure that the next workspace build uses the same provider versions as with the |
| 86 | +last build. |
| 87 | + |
| 88 | +To create a new Terraform lock file, run the |
| 89 | +[`terraform init` command](https://developer.hashicorp.com/terraform/cli/commands/init) |
| 90 | +inside a folder containing the Terraform source code for a given template. |
| 91 | + |
| 92 | +This will create a new file named `.terraform.lock.hcl` in the current |
| 93 | +directory. When you next run |
| 94 | +[`coder templates push`](../reference/cli/templates_push.md), the lock file will |
| 95 | +be stored alongside with the other template source code. |
| 96 | + |
| 97 | +> Note: Terraform best practices also recommend checking in your |
| 98 | +> `.terraform.lock.hcl` into Git or other VCS. |
| 99 | +
|
| 100 | +The next time a workspace is built from that template, Coder will make sure to |
| 101 | +use the same versions of those providers as specified in the lock file. |
| 102 | + |
| 103 | +If, at some point in future, you need to update the providers and versions you |
| 104 | +specified within the version constraints of the template, run |
| 105 | + |
| 106 | +```console |
| 107 | +terraform init -upgrade |
| 108 | +``` |
| 109 | + |
| 110 | +This will check each provider, check the newest satisfiable version based on the |
| 111 | +version constraints you specified, and update the `.terraform.lock.hcl` with |
| 112 | +those new versions. When you next run `coder templates push`, again, the updated |
| 113 | +lock file will be stored and used to determine the provider versions to use for |
| 114 | +subsequent workspace builds. |
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