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Documentation update: Adding Default Lookup to official docs #636

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Aug 4, 2018
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Documentation update: Adding Default Lookup to official docs #636

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7e3eff2
adding documentation for default lookup, missing when implmeneted in …
Aug 3, 2018
e74f816
modifying lang to be only support environment file
Aug 3, 2018
3ebce19
slight grammer fix
Aug 3, 2018
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26 changes: 24 additions & 2 deletions docs/lookups.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -7,8 +7,8 @@ concept called lookups. A lookup is meant to take a value and convert
it by calling out to another service or system.

A lookup is denoted in the config with the ``${<lookup type> <lookup
input>}`` syntax. If ``<lookup type>`` isn't provided, the default of
``output`` will be used.
input>}`` syntax. If ``<lookup type>`` isn't provided, stacker will
fall back to use the ``output`` lookup .

Lookups are only resolved within `Variables
<terminology.html#variables>`_. They can be nested in any part of a YAML
Expand Down Expand Up @@ -58,6 +58,7 @@ dictionary::
stacker includes the following lookup types:

- `output lookup`_
- `default lookup`_
- `kms lookup`_
- `xref lookup`_
- `rxref lookup`_
Expand Down Expand Up @@ -86,6 +87,27 @@ You can specify an output lookup with the following syntax::

ConfVariable: ${output someStack::SomeOutput}


.. _`default lookup`:

default Lookup
--------------

The ``default`` lookup type will check if a value exists for the variable
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This isn't 100% true, right? It can also be used to give default variables to lookups.

${default ${output MyVpc::VpcId}::vpc-123456}

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I... hadn't, really thought of that. It's an interesting idea. I didn't write the lookup module, so let me dig into it to check if that would work. (Or @troyready could chime in, since he wrote it)

in the environment, then fall back to a default defined in the stacker
config if the environment doesn't contain the variable. This allows defaults
to be set at the config file level, while granting the user the ability
to override that value per environment.

Format of value::
<env_var>::<default value>

For example::
Groups: ${default app_security_groups::sg-12345,sg-67890}
If `app_security_groups` is defined in the environment file, its defined
value will be returned. Otherwise, `sg-12345,sg-67890` will be the returned
value.

.. _`kms lookup`:

KMS Lookup
Expand Down