Proposal: add 'installation_only' flag to roles.

Motivation

It takes many minutes to download and install the software. We can do a little ahead of time, e.g., installing the idm:DL1/* packages, but I know that the roles install a lot of packages and it would be difficult for individuals to keep up to date with changes.

We could save many minutes if we could use an AMI that has already downloaded and installed all of the software required by the role.

Proposal

The preparation follows:

• create a fresh instance
• run 'install' with an 'installation_only' flag set
• create an AMI

(This is easy to do with molecule)

During testing and deployment we could start with that AMI, instead of the official OS image or our customization of it, and jump straight to the configuration. The scripts will still need to verify that the proper software is installed but that's a lot faster than the initial download and installation.

Enhancement

Many of the services require information that's only available at deployment, e.g., the actual hostname and IP address of the host.

However some services are either completely agnostic to the role's properties or only require information that's constant across all instances. E.g., the domain, realm, LDAP properties, etc., will often be the same within a smaller organization. (Or if the decision is made to create a series of AMI images.)

In those cases the preparation step could include initialization of those services when possible. It's unlikely to make a big difference with the server or replica but might greatly simplify the final configuration of the client since so much will already be known by that point.