lang/funcs: Filesystem functions hint about dynamically-generated files #25361
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jbardin
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Jun 24, 2020
The functions that interact with the filesystem are, by design, restricted to reading files that are distributed as a static part of the configuration, and cannot be used to interact with files that are generated dynamically by resources in the configuration. However, new users have often yet developed a correct mental model of how Terraform execution works and are confused by the terse error messages these functions return. As an interim step to help some of those users, this just adds some more commentary to the error message which gives a vague, generic directive to look to attributes of the resource that is generating the file, which should (if it's designed well) export attributes that allow the resulting file to be used effectively with common patterns, such as checksums of the content of the generated file. The error message here is not particularly attractive due to the limitations of the context where it's being returned from, but I'm accepting that here in the interest of keeping this change simple, so we can give a hint about a case that seems to frequently generate new-user questions. We may iterate further on the presentation of this message later.
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Oh, whoops! I guess I missed that file when I was committing. Fixed now, and merging. |
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The functions that interact with the filesystem are, by design, restricted to reading files that are distributed as a static part of the configuration, and cannot be used to interact with files that are generated dynamically by resources in the configuration.
However, new users have often yet developed a correct mental model of how Terraform execution works and are confused by the terse error messages these functions return. As an interim step to help some of those users, this just adds some more commentary to the error message which gives a vague, generic directive to look to attributes of the resource that is generating the file, which should (if it's designed well) export attributes that allow the resulting file to be used effectively with common patterns, such as checksums of the content of the generated file.
This error message is coming from a helper function that is used from
file,templatefile, and all of the functions that can produce hash values from the contents of a file, so all of them will now return this extended error message if they encounter a "file not found" condition.The new error message is vague and not particularly attractive due to the limitations of the context where it's being returned from, but I'm accepting that here in the interest of keeping this change simple, so we can give a hint about a case that seems to frequently generate new-user questions.
This is related to #25162, but since that issue is mainly just a placeholder for "something should be done about this" we'll need to see if this issue is a sufficient "something" by observing if the volume of questions about this changes some time after we release this change.