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Setting up an EVM Gateway node

This guide is for running the EVM Gateway node on Flow. The EVM Gateway implements the Ethereum JSON-RPC specification and is the only node type which accepts EVM client connections.

The EVM Gateway is an unstaked, non-participating edge node which consumes Flow protocol state from the configured Flow Access Node and persists the indexed EVM state locally to service EVM client requests. It submits EVM transactions it receives into the Flow network, wrapped using a Cadence transaction, and mutating EVM state when executed. Non-mutating RPC methods only query the local state index of the gateway and are never forwarded to Access Nodes.

Who Should Run an EVM Gateway​

The EVM Gateway can serve as both a dedicated private RPC endpoint and a performance scaling solution, offering similar capabilities to centralized middleware providers like Infura, Alchemy, etc at a fraction of the cost. This is because EVM Gateway nodes connect directly to the Flow network with no middle layer in between.

Applications which generate high call volumes to the JSON-RPC and which may have hit rate limits can benefit from running their own gateway. Self-hosted gateways are dedicated to the operator, enabling the removal of rate limits. Self-hosted gateways connect directly to your chosen Access Node, which you can also run if desired.

Hardware specifications​

TBD

How To Run EVM Gateway

Step 1 - Account Creation​

The EVM Gateway's role in mediating EVM transactions over to Cadence is how it accrues fees from handling client transactions. Since the gateway submits Cadence transactions wrapping EVM transaction payloads to the Flow Access Node the transaction fee for that must be paid by the EVM Gateway.

The account used for funding gateway Cadence transactions must be a COA, not an EOA. --coa-address is configured with the Cadence address of the COA account and the --coa-key must belong to the same account. The --coinbase account accrues EVM Gateway fees from EVM client transactions and can be either an EVM EOA or COA address.

It is acceptable to create a single Cadence account for the COA and use the EVM address associated with that for the COINBASE address.

Create Flow account to use for COA​

If you don't already have a Flow account you will need to create one.

  1. Install Flow Wallet
  2. Once installed you will be able to copy the wallet address, similar to 0x1844efeb3fef2242
  3. Obtain account private key from 
    Settings -> Account List -> Choose Main account -> Private Key -> [Password prompt]
  4. Ensure the wallet is funded from a CEX or other wallet

Step 2 - Build the gateway​

To run EVM Gateway on bare metal or in a VM without the use of docker, select the 'Build from source' tab otherwise refer to the 'Build using Docker' tab.

This will build the EVM gateway binary from source.

For live networks we recommend using the latest release tag.


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git clone https://github.com/onflow/flow-evm-gateway.git
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cd flow-evm-gateway
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git checkout $(curl -s https://api.github.com/repos/onflow/flow-evm-gateway/releases/latest | jq -r .tag_name)
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CGO_ENABLED=1 go build -o evm-gateway cmd/main/main.go
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chmod a+x evm-gateway
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mv evm-gateway /usr/bin

Step 3 - Start Your Node​

Operators will need to refer to the gateway configuration flags and make adjustments that align with the desired deployment topology.

EVM Coinbase address​

If this is your first time setting up the gateway we need to ensure that an EVM COA or EOA address is available to configure the COINBASE. This account can be an account created using Metamask or other web3.js wallet, or otherwise can be the EVM address corresponding to the Flow Wallet COA account created above.

If you haven't already got an EVM address and you have the COA account created by Flow Wallet above then follow the steps below:

  • Click top left burger icon to show current profile
  • Click 'Enable the path to EVM on Flow' button
  • Your EVM account will now be available to use in the left nav account view
  • When you switch to that account you can obtain its EVM address

COA Address and Key​

COA address and private key is configured for --coa-address & --coa-key configuration flags. If running multiple EVM Gateway hosts it is standard to share the same COA address and key across n hosts.

Run the gateway​

Ensure that the following ENV variables have been set. Add/update as required if your configuration differs from those listed.


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# Set required environment variables
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export ACCESS_NODE_GRPC_HOST="access.mainnet.nodes.onflow.org:9000" # or access.devnet.nodes.onflow.org:9000 for testnet
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export FLOW_NETWORK_ID="flow-mainnet" # or flow-testnet
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export INIT_CADENCE_HEIGHT="88226267" # 211176670 for testnet
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export COINBASE="${EVM_ADDRESS_WITHOUT_0x}"
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export COA_ADDRESS="${CADENCE_ACCOUNT_ADDRESS_WITHOUT_0x}"
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export COA_KEY="${CADENCE_ACCOUNT_PRIVATE_KEY_WITHOUT_0x}"
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export GAS_PRICE="100"

Create EVM Gateway service


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sudo tee <<EOF >/dev/null /etc/systemd/system/gateway.service
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[Unit]
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Description=Gateway daemon
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After=network-online.target
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[Service]
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User=$USER
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ExecStart=/usr/bin/evm-gateway \
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--access-node-grpc-host=$ACCESS_NODE_GRPC_HOST \
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--flow-network-id=$FLOW_NETWORK_ID \
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--init-cadence-height=$INIT_CADENCE_HEIGHT \
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--ws-enabled=true \
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--coinbase=$COINBASE \
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--coa-address=$COA_ADDRESS \
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--coa-key=$COA_KEY \
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--rate-limit=9999999 \
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--rpc-host=0.0.0.0 \
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--gas-price=$GAS_PRICE
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Restart=always
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RestartSec=3
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LimitNOFILE=4096
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[Install]
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WantedBy=multi-user.target
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EOF
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cat /etc/systemd/system/gateway.service
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sudo systemctl enable gateway

Start all services


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sudo systemctl daemon-reload
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sudo systemctl restart access-node
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sudo systemctl restart gateway

Check logs


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# change log settings to persistent if not already
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sed -i 's/#Storage=auto/Storage=persistent/g' /etc/systemd/journald.conf
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sudo systemctl restart systemd-journald
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journalctl -u gateway.service -f -n 100

Startup bootstrap indexing​

Once your EVM Gateway is up and running you will see it indexing the Flow network which was configured. At the present time this is a lengthy process (possibly 1-3 days, depending on CPU core count) during which time the gateway will not respond to queries. Once the data is fully indexed the gateway can serve requests to clients.

To speed up gateway setup we recommend backing up the /${GATEWAY_HOME_DIR}/data directory to use when creating additional nodes using the same release version. We are currently working on an export/import feature that will enable gateway operators to store state snapshots to bootstrap newly created nodes without the delay.

Account and Key Management​

EVM Gateway allows for Google and AWS Key Management Service (KMS) setup, which is the recommended way of setting up the gateway for live networks. We recommend creating multiple KMS keys for the same Flow account (ideally 10 or more), how many depends on the desired transaction throughput, since the keys are used in rotation when submitting the transactions. If too few keys are configured it may result in sequence number collisions if the same key is used concurrently by multiple EVM client requests.

KMS Configuration​


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--coa-cloud-kms-project-id=your-project-kms-id \
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--coa-cloud-kms-location-id=global \
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--coa-cloud-kms-key-ring-id=your-project-kms-key-ring-id \
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--coa-cloud-kms-keys=example-gcp-kms1@1,example-gcp-kms2@1 \

Monitoring and Metrics​

The EVM Gateway reports Prometheus metrics which are a way to monitor the gateway's availability and progress. The database folder size may also need to be monitored to prevent disk full issues.

Metric labels


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evm_gateway_api_errors_total # Total count of API errors for period
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evm_gateway_api_request_duration_seconds_bucket # Histogram metric buckets for API request durations
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evm_gateway_api_request_duration_seconds_count # Histogram metric API request count for period
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evm_gateway_api_request_duration_seconds_sum # Histogram metric API request sum of values for period
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evm_gateway_api_server_panics_total # Total count of server panics for period
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evm_gateway_blocks_indexed_total # Total count of EVM blocks indexed
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evm_gateway_cadence_block_height # Cadence block height
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evm_gateway_evm_account_interactions_total # Count of unique accounts observed for period
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evm_gateway_evm_block_height # EVM block height
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evm_gateway_operator_balance # Gateway node COA operator account balance
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evm_gateway_trace_download_errors_total # Total count of trace download errors
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evm_gateway_txs_indexed_total # Total count of indexed transactions

Alerts are recommended to be configured on server panics, low operator balance, and disk usage metrics.

Metrics port​


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--metrics-port 8080 \

Node Status​

For basic node status or keepalive monitoring we recommend automated checks on the following monotonically increasing counter:


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curl -s -XPOST 'your-evm-gw-host:8545' --header 'Content-Type: application/json' --data-raw '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}' | jq -r '.result' | xargs printf "%d\n"
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10020239

Troubleshooting​

State stream configuration​

If you are running an Access Node on the same logical host as the EVM Gateway you may see ehe following log entries.


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failure in event subscription at height ${INIT-CADENCE-HEIGHT}, with: recoverable: disconnected: error receiving event: rpc error: code = Unimplemented desc = unknown service flow.executiondata.ExecutionDataAPI”


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component execution data indexer initialization failed: could not verify checkpoint file: could not find expected root hash e6d4f4c755666c21d7456441b4d33d3521e5e030b3eae391295577e9130fd715 in checkpoint file which contains: [e10d3c53608a1f195b7969fbc06763285281f64595be491630a1e1bdfbe69161]

To resolve this configure --state-stream-addr to use the same address/port combination which is set for Access Node --rpc-addr. This is required by the gateway to allow both the streaming and non-streaming APIs to query using the same connection.

Access Node not fully synced​

The following log entry will occur when the EVM Gateway attempts to sync with the Access Node but it has not yet synced up to latest block


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failure in event subscription at height ${INIT-CADENCE-HEIGHT}, with: recoverable: disconnected: error receiving event: rpc error: code = FailedPrecondition desc = could not get start height: failed to get lowest indexed height: index not initialized

FAQs​

TBD