How do I decide what kind of component to create?

How do you decide whether you should be creating a module, a deployable architecture, or a deployable architecture stack? Let's compare the differences and evaluate the use cases in the following sections to help you decide.

Comparing deployable architectures and modules

The following table provides a comparison and quick summary of the key differences between modules and types of deployable architectures.

Comparison of concepts
	Scope	Coupling	Deployable	Author
Module	Narrow	Tight	No	Developer
Deployable architecture	Medium to broad	Tight	Yes	Developer
Deployable architecture stack	Broad	Loose	Yes	Anyone

The following table can help you decide whether to use a module, a deployable architecture, or a deployable architecture stack depending on your use case.

Help me choose the component to use
Purpose	Recommended component	Notes
Accelerate coding automation	Modules	Modules provide reusable, curated automation to get developers of deployable architectures coding faster. Modules are for developers, not consumers.
Ensure that the cloud is secure and compliant	Deployable architecture	Deployable architectures enforce security and compliance for an architecture. If a deployable architecture is too small in scope, it cannot enforce compliance. For example, a deployable architecture that deploys only a virtual server instance can't ensure network security.
Give users a choice with guardrails	Stacked deployable architecture	With stacked deployable architectures, you can swap deployable architectures or add on deployable architectures and give users more choices. Since deployable architectures enforce security and compliance, stacking helps ensure the overall solution remains compliant. Stacked deployable architectures are excellent for things like selecting which database to use.
User-created solutions or architectures	Stacked deployable architectures	Stacked deployable architectures allow users to create and publish their own repeatable patterns that are still safe, as they are composed of secure and compliant deployable architectures.
Decoupled architecture components	Stacked deployable architectures	Deployable architectures can be independently developed and versioned, but then combined into a stacked deployable architecture for deployment.
Simplified user experience	Deployable architecture	Deployable architectures can provide a small or simple list of inputs to the user even for large or complex architectures. Deployable architectures are simple to understand and deploy. In comparison, stacking deployable architectures is a little more complex as the deployable architectures are exposed.

IBM Cloud projects ensure that resources are deployed through deployable architectures from the catalog and operate within the security and compliance guardrails of the organization. They also ensure that these resources are kept up to date and do not drift.

Dependencies for deployable architectures

Dependencies arise when resources that are provisioned by one deployable architecture are required by another. That is, the resources that one deployable architecture provisions are used during the deployment of another architecture, as illustrated in the following image.

A visual representation of a deployable architecture with a dependency. Deployable architecture A outputs resources that are then used as inputs in deployable architecture B. — Deployable architecture dependencies

One way to work with dependencies is to stack deployable architectures and add references between them in a project. For example, the VSI on VPC landing zone deployable architecture includes a variation that extends the Red Hat OpenShift Container Platform on VPC landing zone deployable architecture. Consider stacking these architectures together in a project. This approach works well if the prerequisite architecture isn't deployed yet. You also don't need to edit code to stack deployable architectures.

Many deployable architectures are stand-alone and aren't extensions of other architectures, but you can choose to extend some deployable architectures in the Architecture section of the catalog details page. Select an option from the How do you want to build this architecture? menu.

However, if you already deployed Red Hat OpenShift Container Platform and you need to deploy VSI, the resources that are required for VSI are already provisioned. You don't need to deploy the Red Hat OpenShift Container Platform architecture again. Since the VSI architecture is an extension of the Red Hat OpenShift Container Platform, you can deploy VSI and the architecture uses the resources from the Red Hat OpenShift Container Platform as needed.

For more information, see Specifying dependencies.

Terraform versus Ansible

In IBM Cloud, a deployable architecture must use Terraform to declare the inputs and outputs of the deployable architecture (the interface) as Ansible does not have a machine-readable interface definition. Otherwise, the author of a deployable architecture might use any combination of Ansible pre- or post-scripts and Terraform to run the work of the deployable architecture. So, how does a developer decide which technology to use and for what?

Comparison of configuration languages
The first column are categories used to compare Terraform and Ansible. The second column provides information about how Terraform relates to the set category in column one and the third column provides information about how Ansible relates to the set category in column one.
	Terraform	Ansible
Language	Declarative	Procedural
Syntax	HCL (similar to JSON)	YAML (and callouts to other scripts)
Default approach	Mutable infrastructure	Immutable infrastructure
Focus	Infrastructure	Configuration
Drift	Comparison with wanted state	Idempotent tasks

Terraform is excellent at creating and managing infrastructure, whereas Ansible is excellent at configuring the software and operating systems that are running on that infrastructure. Because Ansible is procedural, you can also script one-time operations. Maintenance tasks, like restoring from backup, are easy in Ansible.

Help me choose the configuration language to use
Purpose	Recommended configuration language	Notes
Deploy cloud infrastructure or services	Terraform	Terraform targets this use case and is better at handling changing infrastructure. IBM Cloud provides Terraform modules and supported deployable architectures to accelerate secure and compliant infrastructure patterns. The Terraform state model allows developers to preview the changes. Those changes can be scanned for compliance.
Install or configure software	Ansible	If a pre-built container or virtual machine image is not suitable for the use case, Ansible is better at handling the software installation and configuration. Ansible has extensive support for automated operations such as configuration edits, package management, and process restarts. A large library of Ansible modules and playbooks are available to ease the configuration of thousands of commonly used software packages.
CCDB integration	Ansible	Making a dynamic call to an on-premises service like a CCDB can be done in Terraform or Ansible but is easier to accomplish in a procedural or scripting language.
Input validation	Terraform or Ansible	Terraform has limited ability to do input validation, but it is declarative and can be used by user interfaces. Ansible adds the ability to do dynamic input validation where inputs to a deployable architecture are checked against a remote service.
Day 2 maintenance actions	Ansible	Day 2 maintenance is generally procedural in nature and best completed in Ansible. Examples include manual backup, restore, or key rotations.
Drift management	Terraform Ansible	Terraform can be used to determine whether drift occurred and what that drift is, which can help you decide how to manage the drift. The drift information is powerful because it might indicate that you can add a change to automation. Ansible can't detect drift. But by regularly reapplying an idempotent ansible script, you can prevent drift.

For more information about including pre- or post-scripts with your deployable architectures, see Creating scripts for deployable architecture.

Next steps: Deciding where to publish

After you've planned out your architecture and decided what type of component to create, you should consider where you plan to share or publish your solution, so that other users can take advantage of the solution that you create. Depending on where you plan to share or publish, you might have different levels of requirements or approvals to complete.