» Consul Connect

Consul Connect provides service-to-service connection authorization and encryption using mutual Transport Layer Security (TLS). Applications can use sidecar proxies in a service mesh configuration to automatically establish TLS connections for inbound and outbound connections without being aware of Connect at all.

» Nomad with Consul Connect Integration

Nomad integrates with Consul to provide secure service-to-service communication between Nomad jobs and task groups. In order to support Consul Connect, Nomad adds a new networking mode for jobs that enables tasks in the same task group to share their networking stack. With a few changes to the job specification, job authors can opt into Connect integration. When Connect is enabled, Nomad will launch a proxy alongside the application in the job file. The proxy (Envoy) provides secure communication with other applications in the cluster.

Nomad job specification authors can use Nomad's Consul Connect integration to implement service segmentation in a microservice architecture running in public clouds without having to directly manage TLS certificates. This is transparent to job specification authors as security features in Connect continue to work even as the application scales up or down or gets rescheduled by Nomad.

» Nomad Consul Connect Example

The following section walks through an example to enable secure communication between a web dashboard and a backend counting service. The web dashboard and the counting service are managed by Nomad. Nomad additionally configures Envoy proxies to run along side these applications. The dashboard is configured to connect to the counting service via localhost on port 9001. The proxy is managed by Nomad, and handles mTLS communication to the counting service.

» Prerequisites

» Consul

Connect integration with Nomad requires Consul 1.6 or later. The Consul agent can be run in dev mode with the following command:

Note: Nomad's Connect integration requires Consul in your $PATH

$ consul agent -dev 

» Nomad

Nomad must schedule onto a routable interface in order for the proxies to connect to each other. The following steps show how to start a Nomad dev agent configured for Connect.

$ sudo nomad agent -dev-connect

» CNI Plugins

Nomad uses CNI plugins to configure the network namespace used to secure the Consul Connect sidecar proxy. All Nomad client nodes using network namespaces must have CNI plugins installed.

The following commands install CNI plugins:

$ curl -L -o cni-plugins.tgz https://github.com/containernetworking/plugins/releases/download/v0.8.1/cni-plugins-linux-amd64-v0.8.1.tgz
$ sudo mkdir -p /opt/cni/bin
$ sudo tar -C /opt/cni/bin -xzf cni-plugins.tgz

» Run the Connect-enabled Services

Once Nomad and Consul are running, submit the following Connect-enabled services to Nomad by copying the HCL into a file named connect.nomad and running: nomad run connect.nomad

 job "countdash" {
   datacenters = ["dc1"]
   group "api" {
     network {
       mode = "bridge"
     }

     service {
       name = "count-api"
       port = "9001"

       connect {
         sidecar_service {}
       }
     }

     task "web" {
       driver = "docker"
       config {
         image = "hashicorpnomad/counter-api:v1"
       }
     }
   }

   group "dashboard" {
     network {
       mode = "bridge"
       port "http" {
         static = 9002
         to     = 9002
       }
     }

     service {
       name = "count-dashboard"
       port = "9002"

       connect {
         sidecar_service {
           proxy {
             upstreams {
               destination_name = "count-api"
               local_bind_port = 8080
             }
           }
         }
       }
     }

     task "dashboard" {
       driver = "docker"
       env {
         COUNTING_SERVICE_URL = "http://${NOMAD_UPSTREAM_ADDR_count_api}"
       }
       config {
         image = "hashicorpnomad/counter-dashboard:v1"
       }
     }
   }
 }

The job contains two task groups: an API service and a web frontend.

» API Service

The API service is defined as a task group with a bridge network:

   group "api" {
     network {
       mode = "bridge"
     }

     ...
   }

Since the API service is only accessible via Consul Connect, it does not define any ports in its network. The service stanza enables Connect:

   group "api" {
     ...

     service {
       name = "count-api"
       port = "9001"

       connect {
         sidecar_service {}
       }
     }

     ...
   }

The port in the service stanza is the port the API service listens on. The Envoy proxy will automatically route traffic to that port inside the network namespace.

» Web Frontend

The web frontend is defined as a task group with a bridge network and a static forwarded port:

   group "dashboard" {
     network {
       mode ="bridge"
       port "http" {
         static = 9002
         to     = 9002
       }
     }

     ...
   }

The static = 9002 parameter requests the Nomad scheduler reserve port 9002 on a host network interface. The to = 9002 parameter forwards that host port to port 9002 inside the network namespace.

This allows you to connect to the web frontend in a browser by visiting http://<host_ip>:9002 as show below:

Count Dashboard

The web frontend connects to the API service via Consul Connect:

     service {
       name = "count-dashboard"
       port = "9002"

       connect {
         sidecar_service {
           proxy {
             upstreams {
               destination_name = "count-api"
               local_bind_port = 8080
             }
           }
         }
       }
     }

The upstreams stanza defines the remote service to access (count-api) and what port to expose that service on inside the network namespace (8080).

The web frontend is configured to communicate with the API service with an environment variable:

       env {
         COUNTING_SERVICE_URL = "http://${NOMAD_UPSTREAM_ADDR_count_api}"
       }

The web frontend is configured via the $COUNTING_SERVICE_URL, so you must interpolate the upstream's address into that environment variable. Note that dashes (-) are converted to underscores (_) in environment variables so count-api becomes count_api.

» Limitations

  • The consul binary must be present in Nomad's $PATH to run the Envoy proxy sidecar on client nodes.
  • Consul Connect Native is not yet supported.
  • Consul Connect HTTP and gRPC checks are not yet supported.
  • Consul ACLs are not yet supported.
  • Only the Docker, exec, and raw exec drivers support network namespaces and Connect.
  • Variable interpolation for group services and checks are not yet supported.
  • Consul Connect and network namespaces are only supported on Linux.