Envoy Use Case: UDP

Envoy allows to accept UDP requests.

The Mia-Platform Console helps to configure the Envoy API Gateway using the advanced section.

With the following configuration we configure the api gateway to accept UDP requests to the port 33333 and forward it to the service udp-server that accepts traffic at the port 33333.

Create the udp listener

- "@type": type.googleapis.com/envoy.config.listener.v3.Listener
  name: udp
  address:
    socket_address:
      protocol: UDP
      address: 0.0.0.0
      port_value: 33333
  udp_listener_config:
    downstream_socket_config:
      max_rx_datagram_size: 9000
  listener_filters: 
    - name: envoy.filters.udp_listener.udp_proxy 
      typed_config:
        "@type": type.googleapis.com/envoy.extensions.filters.udp.udp_proxy.v3.UdpProxyConfig
        stat_prefix: udp_stats  
        cluster: udp_cluster
        idle_timeout: 60s    

This configuration creates a listener named udp that accepts and proxies UDP traffic. The listener monitors on the port 33333 for incoming UDP packets. Configuring the IP address to 0.0.0.0 we are accepting packets from any address.

In this configuration, with the field udp_listener_config.downstream_socket_config.max_rx_datagram_size we set a maximum size for incoming packets to 9000 bytes. If not set, the default is 1500 bytes.

We also define a proxy filter that indicates udp_cluster as cluster to forward the traffic to. The timeout assigned in the proxy filter is of 60 seconds.

Envoy will also create metrics that will have the prefix udp_stats.

Create the udp cluster

We also configure a cluster that defines how Envoy forwards traffic to the desired service.

- "@type": type.googleapis.com/envoy.config.cluster.v3.Cluster
  name: udp_cluster
  connect_timeout: 30s
  type: LOGICAL_DNS
  lb_policy: ROUND_ROBIN
  load_assignment:
    cluster_name: udp_cluster
    endpoints:
      - lb_endpoints:
          - endpoint:
              address:
                socket_address:
                  address: udp-server
                  port_value: 33333   

The configuration creates a cluster udp_cluster that forwards the incoming UDP requests to the service udp-server to the port 33333.

With the connect_timeout field we say that Envoy will wait up to 30 seconds when trying to connect to any endpoint in this cluster. We set LOGICAL_DNS as cluster type which means the endpoints are discovered using DNS resolution, and the DNS results are cached and periodically refreshed.

Finally as load balancing policy we set the standard strategy ROUND_ROBIN.