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Scroll Sequencer Migration

This module contains documentation and scripts for Scroll's sequencer migration from l2geth to rollup node (RN) aka l2reth.

Risks

We want to minimize risks and minimize service disruption. For this we need to consider following risks:

  • invalid L2 blocks produced
  • L2 reorg (e.g. different blocks issued at same L2 block height)
  • L1 messages skipped/reverted
  • general service interruption

Migration Procedure

To instill confidence we will do many repeated transitions from l2geth -> l2reth -> l2geth with the time that l2reth sequences increasing.

The high-level flow of the transition will look like this:

  1. l2geth is sequencing currently
  2. Turn off l2geth sequencing
  3. Get block height of l2geth
  4. Wait until l2reth has same block height
  5. Turn on l2reth sequencing
  6. Wait until l2reth has sequenced until block X or for some time
  7. Turn off l2reth sequencing
  8. Wait until l2geth has same block height
  9. Turn on l2geth sequencing

Usage

Make sure the L2RETH_RPC_URL and L2GETH_RPC_URL env variables are properly configured. Simply run the script and follow the instructions.

./migrate-sequencer.sh <blocks_to_produce>
./revert-l2geth-to-block.sh <block_number>
./switch-to-l2geth.sh

# make common functions available on bash
source common-functions.sh

start_l2geth_mining
get_block_info $L2GETH_RPC_URL
[...]

Testing locally

To test locally run the test docker_test_migrate_sequencer and execute the migrate-sequencer.sh script.

# this test runs for ~60 seconds and starts with l2geth sequencing and expects all nodes to reach the same block at block number 120.
RUST_LOG=info,docker-compose=off cargo test --package tests --test migrate_sequencer -- docker_test_migrate_sequencer --exact --show-output

source local.env
./migrate-sequencer.sh <blocks_to_produce>

# if necessary, reset l2geth block height and start sequencing on l2geth.
./revert-l2geth-to-block.sh <block_number>

Simulating failure case:

  • To simulate the case where l2reth produces invalid blocks we can adjust to --builder.gaslimit=40000000 in launch_rollup_node_sequencer.bash. This will produce a block with a too big jump of the gas limit and l2geth will reject it. In a simulation we can then "revert" l2geth to its latest block and start sequencing on l2geth again.
  • Continuing on the above case we can fabricate a L2 reorg by simply resetting to any previous block. For all l2geth nodes the reorg will be shallow (ie before the invalid l2reth blocks) and for l2reth it will be deeper (ie all l2reth produced blocks + reset to previous block).

Running with Docker

docker run -it --rm sequencer-migration:latest

# then just use the scripts as before
./migrate-sequencer.sh <blocks_to_produce>

# or call any of the common functions
start_l2geth_mining
get_block_info $L2GETH_RPC_URL
[...]

If running on Linux you might need to specify -e L2GETH_RPC_URL=http://your-l2geth:8547 -e L2RETH_RPC_URL=http://your-l2reth:8545 as the default URLs might not work.