add two way communication config for relayer

content/course/interchain-messaging/10-running-a-relayer/05-multichain-relayer-config.mdx

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+---
+title: Two-Way Messaging Configuration
+description: Learn how to configure a relayer for multiple L1s
+updated: 2024-10-09
+authors: [owenwahlgren]
+icon: BookOpen
+---
+
+<Callout>Important: The relayer needs funds on both L1s to deliver messages. </Callout>
+
+### Two-Way Messaging Configuration
+
+In this section, you’ll learn how to configure a relayer to support two-way messaging between multiple Layer 1 blockchains (L1s). By extending your existing configuration, you can enable the relayer to handle communication in both directions, eliminating the need to run multiple relayers.
+
+### Accessing the Relayer Configuration File
+
+The relayer configuration is supplied as a JSON file. To open the configuration file automatically created by the Avalanche-CLI, run the following command:
+```bash
+code ~/.avalanche-cli/runs/network_xxxx_xxxx/awm-relayer-config.json 
+```
+
+<Callout>Replace xxxx_xxxx with the name automatically assigned to your local deployment.</Callout>
+
+Alternatively, navigate to the directory `~/.avalanche-cli/runs/` and locate the relayer configuration file for your network.
+
+### Understanding the Existing Configuration
+
+Assuming you have a configuration as described in the [Relayer Configuration section](/course/interchain-messaging/10-running-a-relayer/04-relayer-configuration), your current configuration should look similar to the following:
+```json
+{
+  "p-chain-api": {
+    "base-url": "http://127.0.0.1:9650",
+    "query-parameters": {},
+    "http-headers": null
+  },
+  "info-api": {
+    "base-url": "http://127.0.0.1:9650",
+    "query-parameters": {},
+    "http-headers": null
+  },  
+  "source-blockchains": [
+    {
+      "subnet-id": "11111111111111111111111111111111LpoYY",
+      "blockchain-id": "epm5fG6Pn1Y5rBHdTe36aZYeLqpXugreyHLZB5dV81rVTs7Ku",
+      "vm": "evm",
+      "rpc-endpoint": {
+        "base-url": "http://127.0.0.1:9650/ext/bc/<blockchain-id>/rpc",
+        "query-parameters": null,
+        "http-headers": null
+      },
+      "ws-endpoint": {
+        "base-url": "ws://127.0.0.1:9650/ext/bc/<blockchain-id>/ws",
+        "query-parameters": null,
+        "http-headers": null
+      },
+      "message-contracts": {
+        "0x0000000000000000000000000000000000000000": {
+          "message-format": "off-chain-registry",
+          "settings": {
+            "teleporter-registry-address": "0x<registry-address>"
+          }
+        },
+        "0x<contract-address>": {
+          "message-format": "teleporter",
+          "settings": {
+            "reward-address": "0x<reward-address>"
+          }
+        }
+      }
+    }
+  ],
+  "destination-blockchains": [
+    {
+      "subnet-id": "11111111111111111111111111111111LpoYY",
+      "blockchain-id": "epm5fG6Pn1Y5rBHdTe36aZYeLqpXugreyHLZB5dV81rVTs7Ku",
+      "vm": "evm",
+      "rpc-endpoint": {
+        "base-url": "http://127.0.0.1:9650/ext/bc/<blockchain-id>/rpc",
+        "query-parameters": null,
+        "http-headers": null
+      },
+      "kms-key-id": "",
+      "kms-aws-region": "",
+      "account-private-key": "<your-private-key>"
+    }
+  ]
+}
+```
+
+### Updating the Configuration for Two-Way Communication
+
+To enable two-way communication between L1s, you need to extend the configuration to include both blockchains in the source-blockchains and destination-blockchains arrays.
+
+Updated Configuration:
+
+```json
+{
+  "p-chain-api": {
+    "base-url": "http://127.0.0.1:9650",
+    "query-parameters": {},
+    "http-headers": null
+  },
+  "info-api": {
+    "base-url": "http://127.0.0.1:9650",
+    "query-parameters": {},
+    "http-headers": null
+  },
+  "source-blockchains": [
+    {
+      "subnet-id": "<blockchain-id-A>",
+      "blockchain-id": "<blockchain-id-A>",
+      "vm": "evm",
+      "rpc-endpoint": {
+        "base-url": "http://127.0.0.1:9650/ext/bc/<blockchain-id-A>/rpc",
+        "query-parameters": null,
+        "http-headers": null
+      },
+      "ws-endpoint": {
+        "base-url": "ws://127.0.0.1:9650/ext/bc/<blockchain-id-A>/ws",
+        "query-parameters": null,
+        "http-headers": null
+      },
+      "message-contracts": {
+        "0x0000000000000000000000000000000000000000": {
+          "message-format": "off-chain-registry",
+          "settings": {
+            "teleporter-registry-address": "0x<registry-address-A>"
+          }
+        },
+        "0x<contract-address-A>": {
+          "message-format": "teleporter",
+          "settings": {
+            "reward-address": "0x<reward-address-A>"
+          }
+        }
+      }
+    },
+    {
+      "subnet-id": "<blockchain-id-B>",
+      "blockchain-id": "<blockchain-id-B>",
+      "vm": "evm",
+      "rpc-endpoint": {
+        "base-url": "http://127.0.0.1:9650/ext/bc/<blockchain-id-B>/rpc",
+        "query-parameters": null,
+        "http-headers": null
+      },
+      "ws-endpoint": {
+        "base-url": "ws://127.0.0.1:9650/ext/bc/<blockchain-id-B>/ws",
+        "query-parameters": null,
+        "http-headers": null
+      },
+      "message-contracts": {
+        "0x0000000000000000000000000000000000000000": {
+          "message-format": "off-chain-registry",
+          "settings": {
+            "teleporter-registry-address": "0x<registry-address-B>"
+          }
+        },
+        "0x<contract-address-B>": {
+          "message-format": "teleporter",
+          "settings": {
+            "reward-address": "0x<reward-address-B>"
+          }
+        }
+      }
+    }
+  ],
+  "destination-blockchains": [
+    {
+      "subnet-id": "<blockchain-id-A>",
+      "blockchain-id": "<blockchain-id-A>",
+      "vm": "evm",
+      "rpc-endpoint": {
+        "base-url": "http://127.0.0.1:9650/ext/bc/<blockchain-id-A>/rpc",
+        "query-parameters": null,
+        "http-headers": null
+      },
+      "kms-key-id": "",
+      "kms-aws-region": "",
+      "account-private-key": "<your-private-key-A>"
+    },
+    {
+      "subnet-id": "<blockchain-id-B>",
+      "blockchain-id": "<blockchain-id-B>",
+      "vm": "evm",
+      "rpc-endpoint": {
+        "base-url": "http://127.0.0.1:9650/ext/bc/<blockchain-id-B>/rpc",
+        "query-parameters": null,
+        "http-headers": null
+      },
+      "kms-key-id": "",
+      "kms-aws-region": "",
+      "account-private-key": "<your-private-key-B>"
+    }
+  ]
+}
+```
+### Explanation of Changes
+
+By adding both blockchains to the source-blockchains and destination-blockchains arrays, the relayer is configured to:
+
+- Listen for messages on both blockchains.
+- Relay messages to the opposite blockchain.
+
+This setup enables two-way communication between the blockchains using a single relayer instance.
+
+### Important Considerations
+
+- **Private Keys**: Ensure that the account-private-key field contains the private key for the respective blockchain. This key is used to sign transactions when relaying messages.
+- **Funding**: The relaxyer account must have sufficient funds on both L1s to cover transaction fees.
+
+### Next Steps
+
+After updating the configuration file:
+- Save the changes.
+- Restart the relayer to apply the new configuration.
+- Test the two-way communication by sending messages between the blockchains.