Here is a comparison of a legacy transaction and an EIP-1559 transaction:

Transaction fee:

A legacy transaction fee is calculated as: gasPrice x gasUsed
An EIP-1559 transaction fee is calculated as: (baseFee + gasTipCap) x gasUsed, see: metamask doc)
From the perspective of CCTX fee charging: gasPrice == baseFee + gasTipCap

In order to not touch the CCTX fee charging logic, zetaclient can simply post (baseFee + maxPriorityFeePerGas) as a replacement of gasPrice for EIP-1559 enabled chains.

Transaction building:

A legacy transaction requires: gasPrice, gasLimit
An EIP-1559 transaction requires: gasTipCap, maxFeePerGas, gasLimit
Sending a EIP-1559 transaction without explicit gasTipCap or maxFeePerGas will result in error (in live tests).

Where to get deterministic numbers of gasTipCap and maxFeePerGas when signing a TSS transaction?
Remember the equation gasPrice == baseFee + gasTipCap. If gasTipCap becomes a field of CCTX outbound parameter, the zetaclient can then calculate baseFee as
gasPrice - gasTipCap.
The maxFeePerGas is the upper limit of gas price that the sender is willing to pay. The estimation of maxFeePerGas can be done by
maxFeePerGas = gasTipCap + baseFee * 2

See this gas fee estimation article: https://www.blocknative.com/blog/eip-1559-fees
See ChainSafe's gas estimator for its bridge: https://github.com/ChainSafe/chainbridge-core/blob/main/chains/evm/calls/evmgaspricer/london.go#L65

The current model of a CCTX outbound parameter only contains gasPrice and gasLimit. To support EIP-1559, a new field gasTipCap needs to be added.

Pending Transaction replacement:

A legacy transaction can be replaced by a new transaction with

same nonce
a higher gasPrice

An EIP-1559 transaction can be replaced by a new transaction with

same nonce
a higher gasTipCap, at least 10% higher
a higher maxFeePerGas, at least 10% higher

See Alchemy doc: https://docs.alchemy.com/docs/retrying-an-eip-1559-transaction
See go-ethereum: https://github.com/ethereum/go- ethereum/blob/87246f3cbaf10f83f56bc4d45f0f3e36e83e71e9/core/txpool/legacypool/list.go#L323
and https://github.com/ethereum/go-ethereum/blob/87246f3cbaf10f83f56bc4d45f0f3e36e83e71e9/core/txpool/legacypool/legacypool.go#L146

When the gas stability pool kicks in:
-both gasPrice and gasTipCap needs to be increased by some percentage >= 10%
-again, remember the equation gasPrice == baseFee + gasTipCap
-zetaclient will calculates new baseFee as: gasPrice - gasTipCap
-zetaclient will calculates new maxFeePerGas as gasTipCap + baseFee * 2
-zetaclient will broadcast updated transaction with new gasTipCap and maxFeePerGas.

Two tasks to switch to EIP-1559

Zetacore side adds a GasTipCap field to MsgVoteGasPrice, so the gas price store can track in state. Also, add a GasTipCap to CCTX outbound parameter. On CCTX creation, populate the median value similar to what we do for gasPrice. In gas stability pool, refresh the GasTipCap accordingly.
Zetaclient side feeds the GasTipCap to zetacore and then use the GasTipCap in CCTX to build/sign outbound transaction.

Support EIP-1559 transactions with ZetaClient #1952

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Support `EIP-1559` transactions with ZetaClient #1952