Add settings for autoscaling to Bigtable module.

[iht]

Bigtable clusters can now autoscale, adding the corresponding settings to the bigtable-instance.

The default num_workers must be set to null, because setting num_workers cannot be done at the same time as specifying autoscaling_config.

[lcaggio]

At the moment autoscaling_config and num_nodes have a null default.

If not wrong: if the user relies on module defaults, an instance with unset num_nodes will be created (suggested for DEV). I would improve the num_nodes description suggesting to set num_nodes > 0 or set the auto_scaling variable for a prod env.

[iht]

At the moment autoscaling_config and num_nodes have a null default.

If not wrong: if the user relies on module defaults, an instance with unset num_nodes will be created (suggested for DEV). I would improve the num_nodes description suggesting to set num_nodes > 0 or set the auto_scaling variable for a prod env.

If not num_nodes nor autoscaling_config are set, the creation of the instance fails because the number of nodes is understood to be zero (default value is null). So the user is safe, no instance would be created in that situation.

I have added some more remarks about this situation in the documentation.

See commits e05dec9 and 59e1d13.

[lcaggio]

I see. In this case, the user has to set an optional variable otherwise the module won't work.

What about having a logic to not set num_nodes on the resource if the value is null? This should create a resource suitable for DEV (see resource documentation)

[lcaggio]

num_nodes = null requires a instance_type configuration. instance_type is deprecated.

I suggest do one of the following:

• set a default to 1 for num_nodes and ignore if autoscaling_config is configured (mentioning the behaviour in the variable description).
• create a single variable with 2 attribute: num_nodes and autoscaling_config and use condition to verify that only one of the 2 is configured.

In both ways the user can have a simple deployment just settings mandatory attributes.

[iht]

num_nodes = null requires a instance_type configuration. instance_type is deprecated.

I suggest do one of the following:

• set a default to 1 for num_nodes and ignore if autoscaling_config is configured (mentioning the behaviour in the variable description).
• create a single variable with 2 attribute: num_nodes and autoscaling_config and use condition to verify that only one of the 2 is configured.

In both ways the user can have a simple deployment just settings mandatory attributes.

I have implemented the first option in commit 5d38e31.

Thanks for the suggestions!

[lcaggio]

Thanks for the PR!

[juliocc]

nice branch name