Tips and Pitfalls on function-hcl

Best Practices

Mon, 01 Jan 0001 00:00:00 +0000

Always use fn-hcl-tools package

Run fn-hcl-tools package to produce your txtar script rather than hand-crafting it. This validates your HCL before it reaches the cluster, catching typos in variable names, bad block structure, and syntax errors at authoring time.

fn-hcl-tools package ./my-composition/

Use locals to name things

Pull commonly-used expressions into top-level locals. This makes the code easier to read and avoids long repeated expressions like req.composite.spec.parameters deep inside resource bodies.

Gotchas

Mon, 01 Jan 0001 00:00:00 +0000

Dashes in identifiers mean you can’t subtract without spaces

HCL allows dashes in identifiers. This means a-b is a single identifier, not a minus b. Use spaces for arithmetic: a - b.

locals {
 my-var = 10 # this is a variable named "my-var"
 result = my-var # refers to the variable, not "my" minus "var"
 diff = a - b # subtraction -- spaces required
}

body is an attribute, not a block

body must use = for assignment. Omitting = turns it into a block, which is a different HCL construct and will produce a schema error.