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Control Plane

This document provides a description of the technologies and open source projects used in Threeport.

This document includes a description each component of the Threeport control plane, including the technologies and open source projects in use.


The Threeport API is the heart of the control plane. All clients and control plane components coordinate their activity and store persistent data through the API.

The API is written with the Go programming language. We chose Go because of its portability, efficiency, built-in concurrency, standard library and ecosystem of 3rd party libraries. It has become the default programming language for cloud native systems and has been used extensively in open source projects like Docker and Kubernetes.

We use the Echo framework because it has useful, performant routing and middleware, is easily extensible and does not contain excessive, obstructive features.

API Database

The Threeport API uses CockroachDB for data persistence. We chose to use a SQL database in general for its transactional and relational capabilities. We chose CockroachDB in particular for its distributed capabilities. Threeport offers a global control plane so resilience is a primary concern. We found CockroachDB to be the best implementation of a distributed SQL database.

Notification Broker

The horizontal scalability of Threeport controllers is enabled by the NATS messaging system. The API uses the NATS server to notify controllers of changes in the system. The controllers use NATS to re-queue reconciliation as needed (when unmet conditions prevent immediate reconciliation) and to place distributed locks on particular objects during reconciliation.

Threeport Agent

The Threeport agent is a Kubernetes operator built using the Kubebuilder SDK. It is informed about Threeport-managed workloads using a custom Kubernetes resource. It then places watches on those resources and collects Events in Kubernetes to report back status on those workloads to the Threeport API.

You can find more information about the Threeport agent in the Threeport developer documentation.

Threeport Controllers

Threeport controllers provide the logic and state reconciliation for the control plane. They are written in Go and model some engineering principles from Kubernetes controllers. When a change is made to an object in the Threeport API, the relevant controller is notified so that it can reconcile the state of the system with the desired state configured for that object.

The primary feature that differentiates Threeport controllers from those in Kubernetes is that Threeport controllers are horizontally scalable. Threeport does not not use a watch mechanism the way Kubernetes does. Instead we use a notification broker that allows notifications to be provided to only one of a set of identical controllers at a time.

AWS Controller

The AWS controller is responsible for managing the following managed services in AWS:

  • Elastic Kubernetes Clusters (EKS): used for Kubernetes Runtime environments to deploy user workloads.
  • Relational Database Service (RDS): available as a dependency when used as a part of an application stack.
  • Simple Storage Service (S3): available as a dependency when used by an application to store objects.

We use a library called aws-builder that was developed for use by Threeport. It uses the v2 SDK for the Go programming language to manage AWS resources. We do not use any intermediate toolchains or libraries such as Pulumi, ACK, Crossplane or Terraform. These are capable tools for certain use cases. However, using the AWS SDK directly gives us the most flexibility and ensures we don't encounter any unsupported operations we might need to perform in managing cloud resources for Threeport users. It also serves as a reference implementation for platform engineers that extend Threeport and wish to use a similar approach.

Control Plane Controller

The control plane controller allows users of Threeport to deploy new Threeport control planes using Threeport itself. This is available so that large organization that wish to clearly separate concerns between lines of business can do so in a Threeport-native way without the need to use qleetctl to bootstrap new control planes when needed. It also allows separation of tiers, e.g. development and production if desired. However, we don't recommend this approach for most users unless they have a compelling need for it.

Gateway Controller

The gateway controller manages network ingress support services when a workload has such a dependency.

The following support services are installed on Kubernetes as needed by the Gateway controller:

  • Gloo Edge: the network ingress controller used by Threeport.
  • cert-manager: used to provision and rotate TLS certificates.
  • external-dns: manages DNS records created for workloads.

When a support service controller needs to be installed in Kubernetes, we use the support-services-operator to perform the install. The Kubernetes manifest provided to the Workload is actually a custom resource that is managed by the support-services-operator. It installs the support services listed above in this manner.

In addition to the support services installations on Kubernetes, the gateway controller appends Kubernetes resources to those defined by the user with the Workload resource to configure the support service for that workload.

Helm Workload Controller

The Helm workload controller uses the popular Kubernetes package manager, Helm to deploy workloads in Kubernetes. Helm templates have drawbacks in complex environments since templating is inherently inferior to general purpose programming languages. More on this topic is discussed in the Continuous Delivery & GitOps section of the Application Orchestration document. We prefer Go programs to construct Kubernetes resources. However, Helm support is still valuable because many open-source charts are available and it is already in extensive use by many teams.

Although we prefer Go to manage Kubernetes resources, we recognize there are use-cases where it is more appropriate to use Helm. Threeport's implementation of the Observability Stack is one example. The requirements for observability line up well with what is already provided by open-source Helm charts, so it made more sense to implement this controller with Threeport's Helm integration.

Kubernetes Runtime Controller

The Kubernetes runtime controller is used to provision new Kubernetes environments for workloads. It serves as a cloud provider agnostic abstraction that allows a user to provision environments with the cloud provider as a simple attribute of the KubernetesRuntimeDefinition object. The KubernetesRuntimeInstance object is where connection information for each cluster is stored and utilized when workloads are deployed to that cluster.

Observability Controller

The observability controller is responsible for deploying observability stacks when a Threeport user wishes to have access to metrics and logs from their workloads.

The following components are available to deploy as a part of the stack:

  • Prometheus: the metrics collection system.
  • Promtail: log forwarding from individual machines to the log storage back end.
  • Loki: log storage.
  • Grafana: observability dashboard.

The observability controller leverages the Helm workload controller to install Helm charts to deploy each of these components.

Secrets Controller

The secrets controller is responsible for storing sensitive information in a secret storage system. Currently, the only supported managed service for this is AWS Secret Manager. The secret manager leverages the external-secrets project. This support service is also installed by the support-services-operator when needed. This allows Threeport to expose secrets to running apps as needed by users.

Note: when storing secrets using Threeport, the value of the secret is never stored in the Threeport database. The notifications that contain the secret value are never written to disk by NATS and are encrypted in transit.

Terraform Controller

The Terraform controller uses Terraform to provision custom infrastructure needed by workloads. Terraform is less than ideal for provisioning infrastructure in a control plane like Threeport for reasons discussed elsewhere but it is offered in Threeport for two reasons. Many teams have made extensive use of Terraform and this allows them to use those configs in Threeport. Also, Threeport offers native support for only a small number of AWS managed services and Terraform offers support for a much larger number of those resources. Using Terraform for simpler use cases can be useful compared to the alternative of developing a custom Threeport extension to manage those same AWS resources.

Note: Terraform is only supported for managing AWS resource at this time.

Workload Controller

The workload controller deploys a defined set of Kubernetes resources to a nominated (or default) Kubernetes runtime instance. This controller is quite rudimentary in that the user is required to define the granular detail of all Kubernetes resources that constitute their workload. However, it is useful in simple implementations. When paired with a Kubernetes operator or a custom Threeport controller that abstracts the details of the Kubernetes resources, it is a vital mechanism. It is the primary interface with the Kubernetes API in Threeport.

Next Steps

For a more depth of understanding in how Threeport controllers work, see our Threeport Controllers architecture documentation.