130 lines
3.3 KiB
Markdown
130 lines
3.3 KiB
Markdown
---
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layout: "docs"
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page_title: "Configuration Syntax"
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sidebar_current: "docs-config-syntax"
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description: |-
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The syntax of Terraform configurations is custom. It is meant to strike a balance between human readable and editable as well as being machine-friendly. For machine-friendliness, Terraform can also read JSON configurations. For general Terraform configurations, however, we recommend using the Terraform syntax.
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---
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# Configuration Syntax
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The syntax of Terraform configurations is custom. It is meant to
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strike a balance between human readable and editable as well as being
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machine-friendly. For machine-friendliness, Terraform can also
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read JSON configurations. For general Terraform configurations,
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however, we recommend using the Terraform syntax.
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## Terraform Syntax
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Here is an example of Terraform syntax:
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```
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# An AMI
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variable "ami" {
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description = "the AMI to use"
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}
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/* A multi
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line comment. */
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resource "aws_instance" "web" {
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ami = "${var.ami}"
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count = 2
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source_dest_check = false
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connection {
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user = "root"
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}
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}
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```
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Basic bullet point reference:
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* Single line comments start with `#`
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* Multi-line comments are wrapped with `/*` and `*/`
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* Values are assigned with the syntax of `key = value` (whitespace
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doesn't matter). The value can be any primitive: a string,
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number, or boolean.
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* Strings are in double-quotes.
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* Strings can interpolate other values using syntax wrapped
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in `${}`, such as `${var.foo}`. The full syntax for interpolation
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is
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[documented here](/docs/configuration/interpolation.html).
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* Numbers are assumed to be base 10. If you prefix a number with
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`0x`, it is treated as a hexadecimal number.
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* Numbers can be suffixed with `kKmMgG` for some multiple of 10.
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For example: `1k` is equal to `1000`.
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* Numbers can be suffxed with `[kKmMgG]b` for power of 2 multiples,
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example: `1kb` is equal to `1024`.
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* Boolean values: `true`, `false`, `on`, `off`, `yes`, `no`.
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* Arrays of primitive types can be made by wrapping it in `[]`.
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Example: `["foo", "bar", 42]`.
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* Maps can be made with the `{}` syntax:
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`{ "foo": "bar", "bar": "baz" }`.
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In addition to the basics, the syntax supports hierarchies of sections,
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such as the "resource" and "variable" in the example above. These
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sections are similar to maps, but visually look better. For example,
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these are nearly equivalent:
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```
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variable "ami" {
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description = "the AMI to use"
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}
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# is equal to:
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variable = [{
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"ami": {
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"description": "the AMI to use",
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}
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}]
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```
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Notice how the top stanza visually looks a lot better? By repeating
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multiple `variable` sections, it builds up the `variable` array. When
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possible, use sections since they're visually clearer and more readable.
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## JSON Syntax
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Terraform also supports reading JSON formatted configuration files.
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The above example converted to JSON:
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```json
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{
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"variable": {
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"ami": {
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"description": "the AMI to use"
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}
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},
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"resource": {
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"aws_instance": {
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"web": {
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"ami": "${var.ami}",
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"count": 2,
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"source_dest_check": false,
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"connection": {
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"user": "root"
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}
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}
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}
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}
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}
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```
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The conversion should be pretty straightforward and self-documented.
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The downsides of JSON are less human readability and the lack of
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comments. Otherwise, the two are completely interoperable.
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