In IBC, blockchains do not directly pass messages to each other over the network. This is where relayer comes in. A relayer process monitors for updates on opens paths between sets of IBC enabled chains. The relayer submits these updates in the form of specific message types to the counterparty chain. Clients are then used to track and verify the consensus state.

In addition to relaying packets, this relayer can open paths across chains, thus creating clients, connections and channels.

Additional information on how IBC works can be found here.

**If you are updating the relayer from any version prior to v2.0.0-rc1, your current config file is not compatible. See: config_migration

• Basic Usage - Relaying Across Chains
• Create Path Across Chains
• Troubleshooting
• Features
• Relayer Terminology
• New Chain Implementation
• Recommended Pruning Settings
• Demo

The -h (help) flag tailing any rly command will be your best friend. USE THIS IN YOUR RELAYING JOURNEY.

1. Clone, checkout and install the latest release (releases page).

   Go needs to be installed and a proper Go environment needs to be configured

   $ git clone https://github.com/cosmos/relayer.git
   $ cd relayer && git checkout v2.0.0-rc3
   $ make install

2. Initialize the relayer's configuration directory/file.

   $ rly config init

   Default config file location: ~/.relayer/config/config.yaml

   By default, transactions will be relayed with a memo of rly(VERSION) e.g. rly(v2.0.0).

   To customize the memo for all relaying, use the --memo flag when initializing the configuration.

   $ rly config init --memo "My custom memo"

   Custom memos will have rly(VERSION) appended. For example, a memo of My custom memo running on relayer version v2.0.0 would result in a transaction memo of My custom memo | rly(v2.0.0).

   The --memo flag is also available for other rly commands also that involve sending transactions such as rly tx link and rly start. It can be passed there to override the config.yaml value if desired.

   To omit the memo entirely, including the default value of rly(VERSION), use - for the memo.

3. Configure the chains you want to relay between.

   In our example, we will configure the relayer to operate on the canonical path between the Cosmos Hub and Osmosis.
   
   The rly chains add command fetches chain meta-data from the chain-registry and adds it to your config file.

   $ rly chains add cosmoshub osmosis

   Adding chains from the chain-registry randomly selects an RPC address from the registry entry.
   If you are running your own node, manually go into the config and adjust the rpc-addr setting.

   NOTE: rly chains add will check the liveliness of the available RPC endpoints for that chain in the chain-registry.
   It is possible that the command will fail if none of these RPC endpoints are available. In this case, you will want to manually add the chain config.

   To add the chain config files manually, example config files have been included here

   $ rly chains add --url https://raw.githubusercontent.com/cosmos/relayer/main/docs/example-configs/cosmoshub-4.json cosmoshub
   $ rly chains add --url https://raw.githubusercontent.com/cosmos/relayer/main/docs/example-configs/osmosis-1.json osmosis

4. Import OR create new keys for the relayer to use when signing and relaying transactions.

   key-name is an identifier of your choosing.

   If you need to generate a new private key you can use the add subcommand.

   $ rly keys add cosmoshub [key-name]  
   $ rly keys add osmosis [key-name]  

   If you already have a private key and want to restore it from your mnemonic you can use the restore subcommand.

   $ rly keys restore cosmoshub [key-name] "mnemonic words here"
   $ rly keys restore osmosis [key-name] "mnemonic words here"

5. Edit the relayer's key values in the config file to match the key-name's chosen above.

   This step is necessary if you chose a key-name other than "default"

   Example:

   - type: cosmos
      value:
      key: YOUR-KEY-NAME-HERE
      chain-id: cosmoshub-4
      rpc-addr: http://localhost:26657

6. Ensure the keys associated with the configured chains are funded.

   Your configured addresses will need to contain some of the respective native tokens for paying relayer fees.

   
   You can query the balance of each configured key by running:

   $ rly q balance cosmoshub
   $ rly q balance osmosis

7. Configure path meta-data in config file.
   We have the chain meta-data configured, now we need path meta-data. For more info on path terminology visit here.

   NOTE: Thinking of chains in the config as "source" and "destination" can be confusing. Be aware that most path are bi-directional.

   
   

   rly paths fetch will check for IBC path meta data from the chain-registry and add these paths to your config file.

   $ rly paths fetch

   NOTE: Don't see the path metadata for paths you want to relay on?
   Please open a PR to add this metadata to the GitHub repo!

8. Configure the channel filter.

   By default, the relayer will relay packets over all channels on a given connection.
   
   Each path has a src-channel-filter which you can utilize to specify which channels you would like to relay on.
   
   The rule can be one of three values:

   • allowlist which tells the relayer to relay on ONLY the channels in channel-list
   • denylist which tells the relayer to relay on all channels BESIDES the channels in channel-list
   • empty value, which is the default setting, and tells the relayer to relay on all channels
   
   

   Since we are only worried about the canonical channel between the Cosmos Hub and Osmosis our filter settings would look like the following.
   
   Example:

   hubosmo:
      src:
          chain-id: cosmoshub-4
          client-id: 07-tendermint-259
          connection-id: connection-257
      dst:
          chain-id: osmosis-1
          client-id: 07-tendermint-1
          connection-id: connection-1
      src-channel-filter:
              rule: allowlist
              channel-list: [channel-141]  

   Because two channels between chains are tightly coupled, there is no need to specify the dst channels. If you only know the "dst" channel-ID you can query the "src" channel-ID by running: rly q channel <dst_chain_name> <dst_channel_id> <port> | jq '.channel.counterparty.channel_id'

9. Finally, we start the relayer on the desired path.

   The relayer will periodically update the clients and listen for IBC messages to relay.

   $ rly paths list
   $ rly start [path]

   You will need to start a separate shell instance for each path you wish to relay over.

   When running multiple instances of rly start, you will need to use the --debug-addr flag and provide an address:port. You can also pass an empty string '' to turn off this feature or pass localhost:0 to randomly select a port.

   ---

   [TROUBLESHOOTING]

If you would like to report a security critical bug related to the relayer repo, please reach out @jackzampolin or @Ethereal0ne on telegram.

The Cosmos community is dedicated to providing an inclusive and harassment free experience for contributors. Please visit Code of Conduct for more information.

Create Path Across Chains -->