This is the fourth and last entry in our article series about Caravan, Bitrock’s Cloud-Native Platform based on the HashiCorp stack. Read the first, second and third part on our blog.
The communication layer between application components running on top of Caravan leverages HashiCorp Consul to expose advanced functionalities. Service discovery, health checks, and service mesh are the key features that Consul enables in Caravan.
Service Discovery & Health Checks
While Consul makes it easy to lodge services in its registry, it offers a painless discovery process thanks to the different ways of inspection, such as API, CLO or DNS SRV queries.
The service registry would not be complete without the health checking capabilities. It is possible to set up different kinds of health checks, to inspect whether a service is healthy and thus can be shown as available in the registry. When a health check fails, the registry no longer returns the failed instance in the client queries. In this way the consumer services stop making requests to the faulty instance.
Consul Connect with Envoy
Consul Connect provides Authorization and Encryption of the communication between services using mutual TLS. Applications are not aware of Consul Connect thanks to sidecar proxies deployed next to them to compose a Service Mesh. These proxies "see" all service-to-service traffic and can collect data about it.
Consul Connect uses Envoy proxies and can be configured to collect layer 7 metrics and export them to tools such as Prometheus. Connect uses the registered service identity (rather than IP addresses) to enforce access control with intentions. Intentions declare the source and the destination flow where the connection is allowed - by default all connections are denied following the Zero Trust principles.
Within the Service Mesh, incoming and outgoing communication traffic is handled with a dedicated component called Gateway. The Gateway is secure by default, it encrypts all the traffic and requires explicit intentions to allow the requests to pass through.
Service Mesh in Nomad
Nomad thoroughly integrates with Consul, allowing the specification of Consul configurations inside the Nomad job description. This way operators can define in a single place all the configurations needed to run a Nomad task and to register it in Consul, making it available to other components running in the platform. In detail, Nomad agent automatically registers the service in Consul, sets up its health check, requests dynamic short-lived TLS certificates for a safe in-mesh communication enabled by the Envoy sidecar proxy, whose lifecycle is managed directly by Nomad without any manual intervention required.