[docs] Guide - Connecting Services Across Datacenters (#6052)
* add connect gateway guide * Remove stray space Co-Authored-By: Freddy <freddygv@users.noreply.github.com> * Specify stanza and exact options Co-Authored-By: Freddy <freddygv@users.noreply.github.com> * incorporate comments from freddy * integrate feedback from matt * make snippets all json * incorporate more comments from matt * added links * incorporate comments from neena on google doc draft * make learn lnks relative * clarify that gateways are new * change socat to netcat * add more description about replication token permissions * Apply suggestions from code review Co-Authored-By: Matt Keeler <mkeeler@users.noreply.github.com> * add the prerequisite to enable centralized service config * finish adding docs links
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Judith Malnick
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---
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layout: "docs"
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page_title: "Connecting Services Across Datacenters"
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sidebar_current: "docs-guides-connect-gateways"
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description: |-
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Connect services and secure inter-service communication across datacenters
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using Consul Connect and mesh gateways.
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---
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## Introduction
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Consul Connect is Consul’s service mesh offering, which allows users to observe
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and secure service-to-service communication. Because Connect implements mutual
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TLS between services, it also enabled us to build mesh gateways, which provide
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users with a way to help services in different datacenters communicate with each
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other. Mesh gateways take advantage of Server Name Indication (SNI), which is an
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extension to TLS that allows them to see the destination of inter-datacenter
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traffic without decrypting the message payload.
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Using mesh gateways for inter-datacenter communication can prevent each Connect
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proxy from needing an accessible IP address, and frees operators from worrying
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about IP address overlap between datacenters.
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In this guide, you will configure Consul Connect across multiple Consul
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datacenters and use mesh gateways to enable inter-service traffic between them.
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Specifically, you will:
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1. Enable Connect in both datacenters
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1. Deploy the two mesh gateways
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1. Register services and Connect sidecar proxies
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1. Configure intentions
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1. Test that your services can communicate with each other
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For the remainder of this guide we will refer to mesh gateways as "gateways".
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Anywhere in this guide where you see the word gateway, assume it is specifically
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a mesh gateway (as opposed to an API or other type of gateway).
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## Prerequisites
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To complete this guide you will need two wide area network (WAN) joined Consul
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datacenters with access control list (ACL) replication enabled. If you are
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starting from scratch, follow these guides to set up your datacenters, or use
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them to check that you have the proper configuration:
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- [Deployment Guide](/consul/datacenter-deploy/deployment-guide)
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- [Securing Consul with ACLs](/consul/security-networking/production-acls)
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- [Basic Federation with WAN Gossip](/consul/security-networking/datacenters)
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You will also need to enable ACL replication, which you can do by following the
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[ACL Replication for Multiple
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Datacenters](/consul/day-2-operations/acl-replication) guide with the following
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modification.
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When creating the [replication token for ACL
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management](/consul/day-2-operations/acl-replication#create-the-replication-token-for-acl-management),
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it will need the following policy:
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```json
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{
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"acl": "write",
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"operator": "write",
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"service_prefix": {
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"" : {
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"policy": "read"
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}
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}
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}
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```
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The replication token needs different permissions depending on what you want to
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accomplish. The above policy allows for ACL policy, role, and token replication
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with `acl:write`, CA replication with `operator:write` and intention and
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configuration entry replication with `service:*:read`.
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You will also need to install [Envoy](https://www.envoyproxy.io/) alongside your
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Consul clients. Both the gateway and sidecar proxies will need to get
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configuration and updates from a local Consul client.
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Lastly you should set [`enable_central_service_config =
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true`](https://www.consul.io/docs/agent/options.html#enable_central_service_config)
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on your Consul clients, which will allow them to centrally configrure the
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sidecar and mesh gateway proxies.
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## Enable Connect in Both Datacenters
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Once you have your datacenters set up and ACL replication configured, it’s time
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to enable Connect in each of them sequentially. Connect’s certificate authority
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(which is distinct from the Consul certificate authority that you manage using
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the CLI) will automatically bootstrap as soon as a server with Connect enabled
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becomes the server cluster’s leader. You can also use [Vault as a Connect
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CA](https://www.consul.io/docs/connect/ca/vault.html).
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!> **Warning:** If you are using this guide as a production playbook, we
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strongly recommend that you enable Connect in each of your datacenters by
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following the [Connect in Production
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guide](/consul/developer-segmentation/connect-production),
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which includes production security recommendations.
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### Enable Connect in the primary datacenter
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Enable Connect in the primary data center and bootstrap the Connect CA by adding
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the following snippet to the server configuration for each of your servers.
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```json
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connect {
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"enabled": true
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}
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```
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Load the new configuration by restarting each server one at a time, making sure
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to maintain quorum. This will be a similar process to performing a [rolling
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restart during
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upgrades](https://www.consul.io/docs/upgrading.html#standard-upgrades).
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Stop the first server by running the following [leave
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command](https://www.consul.io/docs/commands/leave.html).
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```text
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$ consul leave
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```
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Once the server shuts down restart it and make sure that it is healthy and
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rejoins the other servers. Repeat this process until you've restarted all the
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servers with Connect enabled.
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### Enable Connect in the secondary datacenter
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Once Connect is enabled in the primary datacenter, follow the same process to
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enable Connect in the secondary datacenter. Add the following configuration to
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the configuration for your servers, and restart them one at a time, making sure
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to maintain quorum.
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```json
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connect {
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"enabled": true
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}
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```
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The `primary_datacenter` setting that was required in order to enable ACL
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replication between datacenters also specifies which datacenter will write
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intentions and act as the [root CA for Connect](https://www.consul.io/docs/connect/connect-internals.html#connections-across-datacenters).
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Intentions, which allow or deny inter-service communication, are automatically
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replicated to the secondary datacenter.
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## Deploy Gateways
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Connect mesh gateways proxy requests from services in one datacenter to services
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in another, so you will need to deploy your gateways on nodes that can reach
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each other over the network. As we mentioned in the prerequisites,
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you will need to make sure that both Envoy and Consul are installed on the
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gateway nodes. You won’t want to run any services on these nodes other than
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Consul and Envoy because they necessarily will have access to the WAN.
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### Generate Tokens for the Gateways
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You’ll need to [generate a
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token](/consul/security-networking/production-acls#apply-individual-tokens-to-the-services)
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for each gateway that gives it read access to the entire catalog.
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Create a file named `mesh-gateway-policy.json` containing the following content.
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```json
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{
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"service_prefix": {
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"": {
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"policy": "read"
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}
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}
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}
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{
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"service": {
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"mesh-gateway": {
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"policy": "write"
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}
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}
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}
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```
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Next, create and name a new ACL policy using the file you just made.
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```text
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$ consul acl policy create \
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-name mesh-gateway \
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-rules @mesh-gateway-policy.json
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```
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Generate a token for each gateway from the new policy.
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```text
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$ consul acl token create -description "mesh-gateway primary datacenter token" \
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-policy-name mesh-gateway
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```
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```text
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$ consul acl token create \
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-description "mesh-gateway secondary datacenter token" \
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-policy-name mesh-gateway
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```
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You’ll apply those tokens when you deploy the gateways.
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### Deploy the Gateway for your primary datacenter
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Register and start the gateway in your primary datacenter with the following
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command.
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```text
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$ consul connect envoy -mesh-gateway -register \
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-service-name "gateway-primary"
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-address "<your private address>" \
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-wan-address "<your externally accessible address>"\
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-token=<token for the primary dc gateway>
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```
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### Deploy the Gateway for your Secondary Datacenter
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Register and start the gateway in your secondary datacenter with the following
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command.
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```text
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$ consul connect envoy -mesh-gateway -register \
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-service-name "gateway-secondary"
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-address "<your private address>" \
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-wan-address "<your externally accessible address>"\
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-token=<token for the secondary dc gateway>
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```
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### Configure Sidecar Proxies to use Gateways
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Next, create a [centralized
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configuration](https://www.consul.io/docs/agent/config_entries/proxy-defaults.html)
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file for all the sidecar proxies in both datacenters called
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`proxy-defaults.json`. This file will instruct the sidecar proxies to send all
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their inter-datacenter traffic through the gateways. It should contain the
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following:
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```json
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{
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"Kind": "proxy-defaults",
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"Name": "global",
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"MeshGateway": "local"
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}
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```
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Write the centralized configuration you just created with the following command.
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```text
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$ consul config write proxy-defaults.json
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```
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Once this step is complete, you will have set up Consul Connect with gateways
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across multiple datacenters. Now you are ready to register the services that
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will use Connect.
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## Register a Service in Each Datacenter to Use Connect
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You can register a service to use a sidecar proxy by including a sidecar proxy
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stanza in its registration file. For this guide, you can use socat to act as a
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backend service and register a dummy service called web to represent the client
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service. Those names are used in our examples. If you have services that you
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would like to connect, feel free to use those instead.
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~> **Caution:** Connect takes its default intention policy from Consul’s default
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ACL policy. If you have set your default ACL policy to deny (as is recommended
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for secure operation) and are adding Connect to already registered services,
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those services may lose connection to each other until you set an intention
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between them to allow communication.
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### Register a back end service in one datacenter
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In one datacenter register a backend service and add an Envoy sidecar proxy
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registration. To do this you will either create a new registration file or edit
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an existing one to include a sidecar proxy stanza. If you are using socat as
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your backend service, you will create a new file called `socat.json` that will
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contain the below snippet. Since you have ACLs enabled, you will have to [create
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a token for the
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service](/consul/security-networking/production-acls#apply-individual-tokens-to-the-services).
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```json
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{
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"service": {
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"name": "socat",
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"port": 8181,
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"token": "<token here>",
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"connect": {"sidecar_service": {} }
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}
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}
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```
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Note the Connect stanza of the registration with the `sidecar_service` and
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`token` options. This is what you would add to an existing service registration
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if you are not using socat as an example.
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Reload the client with the new or modified registration.
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```text
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$ consul reload
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```
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Then start Envoy specifying which service it will proxy.
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```text
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$ consul connect envoy -sidecar-for socat
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```
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If you are using socat as your example, start it now on the port you specified
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in your registration by running the following command.
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```text
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$ socat -v tcp-l:8181,fork exec:"/bin/cat"
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```
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Check that the socat service is running by accessing it using netcat on the same
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node. It will echo back anything you type.
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```text
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$ nc 127.0.0.1 8181
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hello
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hello
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echo
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echo
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```
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Stop the running netcat service by typing `ctrl + c`.
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### Register a front end service in the other datacenter
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Now in your other datacenter, you will register a service (with a sidecar proxy)
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that calls your backend service. Your registration will need to list the backend
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service as your upstream. Like the backend service, you can use an example
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service, which will be called web, or append the connect stanza to an existing
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registration with some customization.
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To use web as your front end service, create a registration file called
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`web.json` that contains the following snippet.
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```json
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{
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"service": {
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"name": "web",
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"port": 8080,
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"token": "<token here>",
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"connect": {
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"sidecar_service": {
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"proxy": {
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"upstreams": [{
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"destination_name": "socat",
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"datacenter": "primary",
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"local_bind_port": 8181
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}]
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}
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}
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}
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}
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}
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```
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Note the Connect part of the registration, which specifies socat as an
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upstream. If you are using another service as a back end, replace `socat` with
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its name and the `8181` with its port.
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Reload the client with the new or modified registration.
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```text
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$ consul reload
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```
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Then start Envoy and specify which service it will proxy.
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```text
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$ consul connect envoy -sidecar-for web
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```
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## Configure Intentions to Allow Communication Between Services
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Now that your services both use Connect, you will need to configure intentions
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in order for them to communicate with each other. Add an intention to allow the
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front end service to access the back end service. For web and socat the command
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would look like this.
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```text
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$ consul intention create web socat
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```
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Consul will automatically forward intentions initiated in the in the secondary
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datacenter to the primary datacenter, where the servers will write them. The
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servers in the primary datacenter will then automatically replicate the written
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intentions back to the secondary datacenter.
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## Test the connection
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Now that you have services using Connect, verify that they can contact each
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other. If you have been using the example web and socat services, from the node
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and datacenter where you registered the web service, start netcat and type
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something for it to echo.
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```text
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$ nc 127.0.0.1 8181
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hello
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hello
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echo
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echo
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```
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## Summary
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In this guide you configured two WAN-joined datacenters to use Consul Connect,
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deployed gateways in each datacenter, and connected two services to each other
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across datacenters.
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Gateways know where to route traffic because of Server Name Indication (SNI)
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where the client service sends the destination as part of the TLS handshake.
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Because gateways rely on TLS to discover the traffic’s destination, they require
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Consul Connect to route traffic.
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### Next Steps
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Now that you’ve seen how to deploy gateways to proxy inter-datacenter traffic,
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you can deploy multiple gateways for redundancy or availability. The gateways
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and proxies will automatically round-robin load balance traffic between the
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gateways.
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If you are using Kubernetes you can configure Connect and deploy gateways for
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your Kubernetes cluster using the Helm chart. Learn more in the [Consul’s
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Kubernetes documentation](https://www.consul.io/docs/platform/k8s/helm.html)
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Visit the Consul documentation for a full list of configurations for [Consul
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Connect](https://www.consul.io/docs/connect/index.html), including [mesh gateway
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configuration options](https://www.consul.io/docs/connect/mesh_gateway.html).
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