187 lines
7.8 KiB
Plaintext
187 lines
7.8 KiB
Plaintext
---
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layout: docs
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page_title: WAN Federation via Mesh Gateways
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description: |-
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WAN federation via mesh gateways allows for Consul servers in different datacenters to be federated exclusively through mesh gateways.
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---
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# WAN Federation via Mesh Gateways
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-> **1.8.0+:** This feature is available in Consul versions 1.8.0 and higher
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~> This topic requires familiarity with [mesh gateways](/docs/connect/gateways/mesh-gateway/service-to-service-traffic-datacenters).
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WAN federation via mesh gateways allows for Consul servers in different datacenters
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to be federated exclusively through mesh gateways.
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When setting up a
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[multi-datacenter](https://learn.hashicorp.com/tutorials/consul/federation-gossip-wan)
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Consul cluster, operators must ensure that all Consul servers in every
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datacenter must be directly connectable over their WAN-advertised network
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address from each other.
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[](/img/wan-federation-connectivity-traditional.png)
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This requires that operators setting up the virtual machines or containers
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hosting the servers take additional steps to ensure the necessary routing and
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firewall rules are in place to allow the servers to speak to each other over
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the WAN.
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Sometimes this prerequisite is difficult or undesirable to meet:
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- **Difficult:** The datacenters may exist in multiple Kubernetes clusters that
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unfortunately have overlapping pod IP subnets, or may exist in different
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cloud provider VPCs that have overlapping subnets.
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- **Undesirable:** Network security teams may not approve of granting so many
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firewall rules. When using platform autoscaling, keeping rules up to date becomes untenable.
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Operators looking to simplify their WAN deployment and minimize the exposed
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security surface area can elect to join these datacenters together using [mesh
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gateways](/docs/connect/gateways/mesh-gateway/service-to-service-traffic-datacenters) to do so.
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[](/img/wan-federation-connectivity-mesh-gateways.png)
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## Architecture
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There are two main kinds of communication that occur over the WAN link spanning
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the gulf between disparate Consul datacenters:
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- **WAN gossip:** We leverage the serf and memberlist libraries to gossip
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around failure detector knowledge about Consul servers in each datacenter.
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By default this operates point to point between servers over `8302/udp` with
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a fallback to `8302/tcp` (which logs a warning indicating the network is
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misconfigured).
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- **Cross-datacenter RPCs:** Consul servers expose a special multiplexed port
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over `8300/tcp`. Several distinct kinds of messages can be received on this
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port, such as RPC requests forwarded from servers in other datacenters.
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In this network topology individual Consul client agents on a LAN in one
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datacenter never need to directly dial servers in other datacenters. This
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means you could introduce a set of firewall rules prohibiting `10.0.0.0/24`
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from sending any traffic at all to `10.1.2.0/24` for security isolation.
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You may already have configured [mesh
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gateways](https://learn.hashicorp.com/tutorials/consul/service-mesh-gateways)
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to allow for services in the service mesh to freely connect between datacenters
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regardless of the lateral connectivity of the nodes hosting the Consul client
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agents.
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By activating WAN federation via mesh gateways the servers
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can similarly use the existing mesh gateways to reach each other without
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themselves being directly reachable.
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## Configuration
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### TLS
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All Consul servers in all datacenters should have TLS configured with certificates containing
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these SAN fields:
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server.<this_datacenter>.<domain> (normal)
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<node_name>.server.<this_datacenter>.<domain> (needed for wan federation)
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This can be achieved using any number of tools, including `consul tls cert create` with the `-node` flag.
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### Mesh Gateways
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There needs to be at least one mesh gateway configured to opt-in to exposing
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the servers in its configuration. When using the `consul connect envoy` CLI
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this is done by using the flag `-expose-servers`. All this does is to register
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the mesh gateway into the catalog with the additional piece of service metadata
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of `{"consul-wan-federation":"1"}`. If you are registering the mesh gateways
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into the catalog out of band you may simply add this to your existing
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registration payload.
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!> Before activating the feature on an existing cluster you should ensure that
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there is at least one mesh gateway prepared to expose the servers registered in
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each datacenter otherwise the WAN will become only partly connected.
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### Consul Server Options
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There are a few necessary additional pieces of configuration beyond those
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required for standing up a
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[multi-datacenter](https://learn.hashicorp.com/tutorials/consul/federation-gossip-wan)
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Consul cluster.
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Consul servers in the _primary_ datacenter should add this snippet to the
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configuration file:
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```hcl
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connect {
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enabled = true
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enable_mesh_gateway_wan_federation = true
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}
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```
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Consul servers in all _secondary_ datacenters should add this snippet to the
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configuration file:
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```hcl
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primary_gateways = [ "<primary-mesh-gateway-ip>:<primary-mesh-gateway-port>", ... ]
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connect {
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enabled = true
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enable_mesh_gateway_wan_federation = true
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}
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```
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The [`start_join_wan`](/docs/agent/config/config-files#start_join_wan) or
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[`retry_join_wan`](/docs/agent/config/config-files#retry_join_wan) are
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only used for the [traditional federation process](/docs/k8s/installation/multi-cluster#traditional-wan-federation).
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They must be omitted when federating Consul servers via gateways.
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-> The `primary_gateways` configuration can also use `go-discover` syntax just
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like `retry_join_wan`.
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### Bootstrapping
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For ease of debugging (such as avoiding a flurry of misleading error messages)
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when intending to activate WAN federation via mesh gateways it is best to
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follow this general procedure:
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### New secondary
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1. Upgrade to the desired version of the consul binary for all servers,
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clients, and CLI.
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2. Start all consul servers and clients on the new version in the primary
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datacenter.
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3. Ensure the primary datacenter has at least one running, registered mesh gateway with
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the service metadata key of `{"consul-wan-federation":"1"}` set.
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4. Ensure you are _prepared_ to launch corresponding mesh gateways in all
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secondaries. When ACLs are enabled actually registering these requires
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upstream connectivity to the primary datacenter to authorize catalog
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registration.
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5. Ensure all servers in the primary datacenter have updated configuration and
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restart.
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6. Ensure all servers in the secondary datacenter have updated configuration.
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7. Start all consul servers and clients on the new version in the secondary
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datacenter.
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8. When ACLs are enabled, shortly afterwards it should become possible to
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resolve ACL tokens from the secondary, at which time it should be possible
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to launch the mesh gateways in the secondary datacenter.
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### Existing secondary
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1. Upgrade to the desired version of the consul binary for all servers,
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clients, and CLI.
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2. Restart all consul servers and clients on the new version.
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3. Ensure each datacenter has at least one running, registered mesh gateway with the
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service metadata key of `{"consul-wan-federation":"1"}` set.
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4. Ensure all servers in the primary datacenter have updated configuration and
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restart.
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5. Ensure all servers in the secondary datacenter have updated configuration and
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restart.
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### Verification
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From any two datacenters joined together double check the following give you an
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expected result:
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- Check that `consul members -wan` lists all servers in all datacenters with
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their _local_ ip addresses and are listed as `alive`.
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- Ensure any API request that activates datacenter request forwarding. such as
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[`/v1/catalog/services?dc=<OTHER_DATACENTER_NAME>`](/api-docs/catalog#dc-1)
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succeeds.
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