FAQ: Hermes v1

[AlianBenabdallah]

Hi Cosmonauts !

This discussion is dedicated to offering answers to frequently asked questions from users. Feel free to ask any question, share and contribute as well !

Can you run multiple Hermes instances concurrently ?

Multiple instances of Hermes can not access to the same wallet concurrently. They would need to coordinate their actions in order to broadcast transactions. If two instances of Hermes operate on the same chain, they need to access different wallets. If you want to run an instance for each channel between two chains, you will need a different pair of wallets for every instance.

What does the refresh client feature do?

As part of the mode.client, Hermes has a refresh feature.

https://github.com/informalsystems/ibc-rs/blob/1d188187721051a34d20841c0146b8c16b5b413b/config.toml#L24

If this feature is enabled, then Hermes will periodically send a UpdateClient message to all clients that are active.

What is an active client?

An active client is defined as a client that an open channel is using. For instance, consider two networks ibc-0 and ibc-1. Suppose there are 3 clients that network ibc-1 is hosting for ibc-0: (1) 07-tendermint-0, 07-tendermint-1, 07-tendermint-2. Suppose there is a single channel open between the two networks: ibc-0 : channel-1 - ibc-1 : channel-2, which is using client 07-tendermint-2 on ibc-1. This means that the other two clients (07-tendermint-0 and 07-tendermint-1) are not in use by any open channel. Upon starting Hermes, those two clients are not considered active and Hermes will not periodically refresh them.

The chains.packet_filter feature will affect which is the set of clients that Hermes considers to be active. If you deny a certain channel, then Hermes will not refresh the clients underlying that channel.

Debug

To debug or understand if your instance of Hermes is correctly performing client refresh, there are 2 ways: inspect the Hermes logs, or inspect the workers.

1. inspect the logs

The line you want to look for is as follows:

2022-07-29T09:19:48.012316Z INFO ThreadId(01) spawned client worker: client::ibc-1->ibc-0:07-tendermint-0

This means that Hermes spawned the client worker for the client existing on chain ibc-0 with identifier 07-tendermint-0, which is verifying headers of network ibc-1.
This log line appears only when Hermes starts-up.

2. inspect the Hermes relayer workers

This method triggers Hermes to dump the state of all its workers, which can then inspect in the logs. To trigger, send a USR1 signal to the Hermes process. Documented here: https://hermes.informal.systems/help.html#inspecting-the-relayer-state

[adizere]

Can you use the default config.toml in production settings?

Briefly, no. The default values in config.toml are not for production, they are just basic heuristics that work most of the time, but in production environments these config options for each chain will require some tuning (depending on the chain). Here are some examples of production configuration (Thanks to CryptoCrew Validators and Notional Labs), which might help:

1. https://github.com/clemensgg/RELAYER-dev-crew/blob/main/HERMES/omniflix/relayer-doc.md
2. https://github.com/notional-labs/notional/blob/master/relaying/hermes/all-ibc.toml
3. https://github.com/cephalopodequipment/config/blob/main/hermes/manual.toml

[adizere]

For testnets, it depends on the networks. For Agoric specifically, here are some details: https://github.com/Agoric/agoric-sdk/blob/6b0deac341424da9b1e8badfbf307c37f16b4618/packages/pegasus/demo.md

[AlianBenabdallah]

Moved to https://github.com/informalsystems/ibc-rs/wiki/FAQ---Hermes-v1.
We should also update the guide