1010 Manage Groups of Machines using Clusters

10 Minutes introductory

Learn how Digital Rebar manages infrastructure using IaC resource abstractions like Clusters and Brokers.

This is our most basic IaC learning module that shows the most basic infrastructure management operations in Digital Rebar. Business ROI: Unlike multi-tenant SaaS, Digital Rebar is user operated software: you will never have to open your firewall for us, share sensitive information or upload access credentials.

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Prerequisites

Additional Labs:

• 1005

Concepts

• clusters
• resource_brokers
• machines
• contexts

Summary

Use IaC to create a group of machines that are coordinated using an dedicated lifecycle workflow object. In Digital Rebar, that known as a "cluster"

Creating a Cluster

1. Navigate to the Clusters view
2. Click the Add Button. Name your Cluster lab1010

   Set `broker/name` Parameter to `context-broker`
   
   Change `cluster/count` if you want more or less than 3 machines
   
   Click `Save`
   
   We will reconfigure the `cluster/count` in a later step.
   
   Now, watch the [lab1010 Activity
   Tab](ux://clusters/Name:lab1010/activity) for the
   `cluster-provision` task
   

Observing the Operation

Now that you've created a cluster, let's what Digital Rebar is doing as an IaC platform on your behalf.

1. Scan Digital Rebar From Resource Brokers, review the context-broker to observe the Activity

   From [Overview](ux://overview), observe the Cluster Status Heartbeat
   and Runtime Statistics
   
   *Note: The Heartbeat only shows active clusters.  If your cluster has
   completed operations, then it will not appear.*
   
   From [Work Orders](ux://work_orders), observe the Work Order
   activity
   
   From [Machines](ux://machines), observe the newly created
   `lab1010-#` Machines that are part of the `lab1010` cluster
   

2. Observe that the your lab1010 Machines and cluster have shared profile (lab1010). The shared profile is created when you created the lab and stores information that becomes accessible to the machines in the cluster because the cluster's profile is also assigned to the machines. A share profile is common Digital Rebar practice used to create a shared working configuration between different IaC components.

3. From one of your lab1010 Machines, use the "Cluster" field to navigate back to the lab1010 cluster. Digital Rebar stores the relationship between a machine and the cluster(s) that are managing it in the cluster/tags Param.

   While looking at the `cluster/tags` Param, you should also note that Digital Rebar also tracks information about the broker that created it in Params like `broker/name`.
   
   Params are used extensively throughout the platform to capture data about systems and their relationships.
   

Resizing your lab1010 Cluster

In Day 2 IaC, we must assume that everything we create will be modified. In this step, we'll show how to resize the cluster you just created. Digital Rebar deliberately separates configuration and action operations. That ensures that you have time to complete all configuration changes before Digital Rebar begins making changes. Future labs will show you how to use Triggers to act immediately on changes.

1. Drain the lab1010 Cluster Change the cluster/count value to 0

   Select and Apply the `universal-application-base-cluster` Blueprint.
   
   The [lab1010 Machines](ux://clusters/Name:lab1010/machines) tab should not have any more machines listed.
   
   It is acceptable to have an empty cluster (count = zero) with no machines.
   
   This is different from deleting the cluster because all of the cluster APIs and configuration are available in an empty cluster.  In an IaC sense, you can completely drain all the resources from a cluster and then reconstruct the cluster later by simply increasing the count.
   

2. Resize and Update lab1010 Cluster Change the cluster/count value to 5

   Select and Apply the `universal-application-base-cluster` Blueprint.
   
   This will cause the cluster to re-evaluate it's configuration.
   
   You can watch the change from the [lab1010 Machines](ux://clusters/Name:lab1010/machines) tab
   
   If you try different `cluster/count`, you will notice that Digital Rebar will add or remove machines during the re-evaluation phase.
   
   Note: Future labs will explain how to control the naming of machines in your cluster.
   

Cleanup your cluster

Releasing resources is a critical part of the IaC story. When you cleanup your cluster, Digital Rebar invokes the Workflow defined in on-delete-workflow to automatically decommission the cluster. This includes telling the associated resource broker to remove all the associated machines. It's important to understand, this is intentional IaC behavior that was added on your behalf when you created the cluster. If you delete a cluster without this setting, then it will leave the associated machines in place. This is also helpful if you've made a mistake with your lab and need to reset and start over.

1. From the Clusters table Select row with lab1010 (a checkbox will appear)

   Use the Actions list to return your Cluster to **Workflow Mode**
   
   Use the Actions list to **Cleanup** your cluster (the related machines
   will be automatically removed also)