Relayer

The Cosmos IBC relayer package contains a basic relayer implementation that is meant for users wishing to relay packets/data between sets of IBC enabled chains. In addition, it is intended as an example where anyone who is interested in building their own relayer can come for complete, working, examples.

NOTE: The relayer is in alpha and is not production ready. If it is used in production, it should always be run in a secure environment and only with just enough funds to relay transactions. Security critical operations should manually verify that the client identifier used in the configuration file corresponds to the correct initial consensus state of the counterparty chain. This can be done by querying the initial consensus state and the header of the counterparty and verifying that the root and hash of the next validator set match. This can be considered equivalent to checking the sha hash of a download or a GPG signature.

Security Notice

If you would like to report a security critical bug related to the relayer repo, please send an email to [email protected]

Code of Conduct

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

Testnet

If you would like to join a relayer testnet, please check out the instructions.

Compatibility Table:

NOTE:

chain	tests	supported ports
gaia		transfer

Features

The relayer supports the following:

• creating/updating IBC Tendermint light clients
• creating IBC connections
• creating IBC transfer channels.
• initiating a cross chain transfer
• relaying a cross chain transfer transaction, its acknowledgement, and timeouts
• relaying from state
• relaying from streaming events
• sending an UpgradePlan proposal for an IBC breaking upgrade
• upgrading clients after a counterparty chain has performed an upgrade for IBC breaking changes

The relayer currently cannot:

• create clients with user chosen parameters (such as UpgradePath)
• submit IBC client unfreezing proposals
• monitor and submit misbehaviour for clients
• use IBC light clients other than Tendermint such as Solo Machine
• connect to chains which don't implement/enable IBC
• connect to chains using a different IBC implementation (chains not using SDK's x/ibc module)

Relayer Terminology

A Path in the relayer represents one very specific path followed to get from one chain to another. Two chains may have many different paths between them. Any path with different clients, connections, or channels are considered unqiuely different and non-fungible.

When using with live networks, it is advised to pre-select your desired parameters for your client, connection, and channel. The relayer will automatically reuse any existing clients that match your configurations since clients, connections, and channels are public goods (no one has control over them).

Recommended Pruning Settings

The relayer relies on old headers and proofs constructed at past block heights to facilitate IBC. For this reason, connected full nodes are recommended to prune old blocks once they have passed the unbonding period of the chain.

Here are the settings used to configure SDK based nodes:

--pruning=custom --pruning-keep-recent=362880 --pruning-keep-every=0 --pruning-interval=100

362880 (3*7*24*60*60 / 5 = 362880) represents a 3 week unbonding period (assuming 5 seconds per block).

Note:

--pruning-keep-every=0 --pruning-interval=100

can be modified to your desired settings.

Pruning nothing is not necessary for a fully functional relayer. Pruning everything will lead to many issues.

Demoing the Relayer

While the relayer is under active development, it is meant primarily as a learning tool to better understand the Inter-Blockchain Communication (IBC) protocol. In that vein, the following demo demonstrates the core functionality which will remain even after the changes:

# ensure go and jq are installed 
# Go Documentation: https://golang.org/doc/install
# jq Documentation: https://stedolan.github.io/jq/download

# First, download and build the gaia source code so we have a working blockchain to test against
$ make get-gaia build-gaia

# two-chainz creates two gaia-based chains with data directories in this repo
# it also builds and configures the relayer for operations with those chains
$ ./scripts/two-chainz
# NOTE: If you want to stop the two gaia-based chains running in the background use `killall gaiad`

# At this point the relayer --home directory is ready for normal operations between
# ibc-0 and ibc-1. Looking at the folder structure of the relayer at this point is helpful
# NOTE: to install tree try `brew install tree` on mac or `apt install tree` on linux
$ tree ~/.relayer

# See if the chains are ready to relay over
$ rly chains list

# See the current status of the path you will relay over
$ rly paths list

# Now you can connect the two chains with one command:
$ rly tx link demo -d -o 3s

# Check the token balances on both chains
$ rly q balance ibc-0
$ rly q bal ibc-1

# Then send some tokens between the chains
$ rly tx transfer ibc-0 ibc-1 1000000samoleans $(rly chains address ibc-1)
$ rly tx relay demo -d

# See that the transfer has completed
$ rly q bal ibc-0
$ rly q bal ibc-1

# Send the tokens back to the account on ibc-0
$ rly tx xfer ibc-1 ibc-0 1000000ibc/27A6394C3F9FF9C9DCF5DFFADF9BB5FE9A37C7E92B006199894CF1824DF9AC7C $(rly ch addr ibc-0)
$ rly tx rly demo -d

# See that the return trip has completed
$ rly q bal ibc-0
$ rly q bal ibc-1

# NOTE: you will see the stake balances decreasing on each chain. This is to pay for fees
# You can change the amount of fees you are paying on each chain in the configuration.

Setting up Developer Environment

Working with the relayer can frequently involve working with local development branches of gaia, akash, cosmos-sdk and the relayer. To setup your environment to point at the local versions of the code and reduce the amount of time in your read-eval-print loops try the following:

1. Set replace github.com/cosmos/cosmos-sdk => /path/to/local/github.com/comsos/cosmos-sdk at the end of the go.mod files for the relayer and gaia. This will force building from the local version of the cosmos-sdk when running the ./dev-env script.
2. After ./dev-env has run, you can use go run main.go for any relayer commands you are working on. This allows you make changes and immediately test them as long as there are no server side changes.
3. If you make changes in cosmos-sdk that need to be reflected server-side, be sure to re-run ./two-chainz.
4. If you need to work off of a gaia branch other than master, change the branch name at the top of the ./two-chainz script.