The RackN team is proud of saying that we left the Orchestration out when we migrated from Digital Rebar v2 to v3. That would mean more if anyone actually agreed on what orchestration means… In this our case, I think we can be pretty specific: Digital Rebar v3 does not manage work across multiple nodes. At this point, we’re emphatic about it because cross machine actions add a lot of complexity and require application awareness that quickly blossoms into operational woe, torture and frustration (aka WTF).

That’s why Digital Rebar focused on doing a simple yet powerful job doing multi-boot workflow on a single machine.

In the latest releases (v3.2+), we’ve delivered an easy to understand stage and task running system that is simple to extend, transparent in operation and extremely fast. There’s no special language (DSL) to learn or database to master. And if you need those things, then we encourage you to use the excellent options from Chef, Puppet, SaltStack, Ansible and others. This is because our primary design focus is planning work over multiple boots and operating system environments instead of between machines. Digital Rebar shines when you need 3+ reboots to automatically scrub, burn-in, inventory, install and then post-configure a machine.

But we may have crossed an orchestration line with our new cluster token capability.

Starting in the v3.4 release, automation authors will be able to use a shared profile to coordinate work between multiple machines. This is not a Digital Rebar feature per se – it’s a data pattern that leverages Digital Rebar locking, profiles and parameters to share information between machines. This allows scripts to elect leaders, create authoritative information (like tokens) and synchronize actions. The basic mechanism is simple: we create a shared machine profile that includes a token that allows editing the profile. Normally, machines can only edit themselves so we have to explicitly enable editing profiles with a special use token. With this capability, all the machines assigned to the profile can update the profile (and only that profile). The profile becomes an atomic, secure shared configuration space.

For example, when building a Kubernetes cluster using Kubeadm, the installation script needs to take different actions depending on which node is first. The first node needs to initialize the cluster master, generate a token and share its IP address. The subsequent nodes must wait until the master is initialized and then join using the token. The installation pattern is basically a first-in leader election while all others wait for the leader. There’s no need for more complex sequencing because the real install “orchestration” is done after the join when Kubernetes starts to configure the nodes.

Our experience is that recent cloud native systems are all capable of this type of shotgun start where all the nodes start in parallel with the minimal bootstrap coordination that Digital Rebar can provide.

Individually, the incremental features needed to enable cluster building were small additions to Digital Rebar. Together, they provide a simple yet powerful management underlay. At RackN, we believe that simple beats complex everyday and we’re fighting hard to make sure operations stays that way.

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