Enabling Service-to-service Traffic Across WAN Federated Datacenters
1.6.0+: This feature is available in Consul versions 1.6.0 and newer.
Mesh gateways enable service mesh traffic to be routed between different Consul datacenters. Datacenters can reside in different clouds or runtime environments where general interconnectivity between all services in all datacenters isn't feasible.
Mesh gateways operate by sniffing and extracting the server name indication (SNI) header from the service mesh session and routing the connection to the appropriate destination based on the server name requested. The gateway does not decrypt the data within the mTLS session.
The following diagram describes the architecture for using mesh gateways for cross-datacenter communication:
Mesh Gateway Tutorial: Follow the mesh gateway tutorial to learn important concepts associated with using mesh gateways for connecting services across datacenters.
Prerequisites
Ensure that your Consul environment meets the following requirements.
Consul
- Consul version 1.6.0 or newer.
- A local Consul agent is required to manage its configuration.
- Consul service mesh must be enabled in both datacenters.
- Each datacenter must have a unique name.
- Each datacenters must be WAN joined.
- The primary datacenter must be set to the same value in both datacenters. This specifies which datacenter is the authority for service mesh certificates and is required for services in all datacenters to establish mutual TLS with each other.
- gRPC must be enabled.
- If you want to enable gateways globally you must enable centralized configuration.
Network
- General network connectivity to all services within its local Consul datacenter.
- General network connectivity to all mesh gateways within remote Consul datacenters.
Proxy
Envoy is the only proxy with mesh gateway capabilities in Consul.
Mesh gateway proxies receive their configuration through Consul, which automatically generates it based on the proxy's registration. Consul can only translate mesh gateway registration information into Envoy configuration.
Sidecar proxies that send traffic to an upstream service through a gateway need to know the location of that gateway. They discover the gateway based on their sidecar proxy registrations. Consul can only translate the gateway registration information into Envoy configuration.
Sidecar proxies that do not send upstream traffic through a gateway are not affected when you deploy gateways. If you are using Consul's built-in proxy as a service mesh sidecar it will continue to work for intra-datacenter traffic and will receive incoming traffic even if that traffic has passed through a gateway.
Configuration
Configure the following settings to register the mesh gateway as a service in Consul.
- Specify
mesh-gateway
in thekind
field to register the gateway with Consul. - Configure the
proxy.upstreams
parameters to route traffic to the correct service, namespace, and datacenter. Refer to theupstreams
documentation for details. The serviceproxy.upstreams.destination_name
is always required. Theproxy.upstreams.datacenter
must be configured to enable cross-datacenter traffic. Theproxy.upstreams.destination_namespace
configuration is only necessary if the destination service is in a different namespace. - Define the
Proxy.Config
settings using opaque parameters compatible with your proxy (i.e., Envoy). For Envoy, refer to the Gateway Options and Escape-hatch Overrides documentation for additional configuration information. - If ACLs are enabled, a token granting
service:write
for the gateway's service name andservice:read
for all services in the datacenter or partition must be added to the gateway's service definition. These permissions authorize the token to route communications for other Consul service mesh services, but does not allow decrypting any of their communications.
Modes
Each upstream associated with a service mesh proxy can be configured so that it is routed through a mesh gateway. Depending on your network, the proxy's connection to the gateway can operate in one of the following modes (refer to the mesh-architecture-diagram):
none
- (Default) No gateway is used and a service mesh sidecar proxy makes its outbound connections directly to the destination services.local
- The service mesh sidecar proxy makes an outbound connection to a gateway running in the same datacenter. That gateway is responsible for ensuring that the data is forwarded to gateways in the destination datacenter. Refer to the flow labeledlocal
in the mesh-architecture-diagram.remote
- The service mesh sidecar proxy makes an outbound connection to a gateway running in the destination datacenter. The gateway forwards the data to the final destination service. Refer to the flow labeledremote
in the mesh-architecture-diagram.
Service Mesh Proxy Configuration
Set the proxy to the preferred mode to configure the service mesh proxy. You can specify the mode globally or within child configurations to control proxy behaviors at a lower level. Consul recognizes the following order of precedence if the gateway mode is configured in multiple locations the order of precedence:
- Upstream definition (highest priority)
- Service instance definition
- Centralized
service-defaults
configuration entry - Centralized
proxy-defaults
configuration entry
Example Configurations
Use the following example configurations to help you understand some of the common scenarios.
Enabling Gateways Globally
The following proxy-defaults
configuration will enable gateways for all mesh services in the local
mode.
Enabling Gateways Per Service
The following service-defaults
configuration will enable gateways for all mesh services with the name web
.
Enabling Gateways for a Proxy Upstream
The following service definition will enable gateways in the local
mode for one upstream, the remote
mode for a second upstream and will disable gateways for a third upstream.