The Flow Emulator is a lightweight tool that emulates the behaviour of the real Flow network.
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The emulator exposes a gRPC server that implements the Flow Access API, which is designed to have near feature parity with the real network API.
The Flow Emulator can be run in different modes and settings, all of them are described in the table bellow.
Please note that if you will run the emulator using the Flow CLI you must use flags to pass configuration values and if you plan to run the emulator with Docker you must use the environment variables (Env) to pass configuration values.
| Flag | Env | Default | Description |
|---|---|---|---|
--port, -p |
FLOW_PORT |
3569 |
RPC port to listen on |
--http-port |
FLOW_HTTPPORT |
8080 |
HTTP port to listen on |
--verbose, -v |
FLOW_VERBOSE |
false |
Enable verbose logging (useful for debugging) |
--block-time, -b |
FLOW_BLOCKTIME |
0 |
Time between sealed blocks. Valid units are ns, us (or µs), ms, s, m, h |
--service-priv-key |
FLOW_SERVICEPRIVATEKEY |
random | Private key used for the service account |
--service-pub-key |
FLOW_SERVICEPUBLICKEY |
random | Public key used for the service account |
--service-sig-algo |
FLOW_SERVICEKEYSIGALGO |
ECDSA_P256 |
Service account key signature algorithm |
--service-hash-algo |
FLOW_SERVICEKEYHASHALGO |
SHA3_256 |
Service account key hash algorithm |
--init |
FLOW_INIT |
false |
Generate and set a new service account |
--grpc-debug |
FLOW_GRPCDEBUG |
false |
Enable gRPC server reflection for debugging with grpc_cli |
--persist |
FLOW_PERSIST |
false | Enable persistence of the state between restarts |
--dbpath |
FLOW_DBPATH |
./flowdb |
Specify path for the database file persisting the state |
--simple-addresses |
FLOW_SIMPLEADDRESSES |
false |
Use sequential addresses starting with 0x1 |
--token-supply |
FLOW_TOKENSUPPLY |
1000000000.0 |
Initial FLOW token supply |
--transaction-expiry |
FLOW_TRANSACTIONEXPIRY |
10 |
Transaction expiry, measured in blocks |
--storage-limit |
FLOW_STORAGELIMITENABLED |
true |
Enable account storage limit |
--storage-per-flow |
FLOW_STORAGEMBPERFLOW |
Specify size of the storage in MB for each FLOW in account balance. Default value from the flow-go | |
--min-account-balance |
FLOW_MINIMUMACCOUNTBALANCE |
Specify minimum balance the account must have. Default value from the flow-go | |
--transaction-fees |
FLOW_TRANSACTIONFEESENABLED |
false |
Enable transaction fees |
--transaction-max-gas-limit |
FLOW_TRANSACTIONMAXGASLIMIT |
9999 |
Maximum gas limit for transactions |
--script-gas-limit |
FLOW_SCRIPTGASLIMIT |
100000 |
Specify gas limit for script execution |
The emulator is bundled with the Flow CLI, a command-line interface for working with Flow.
Follow these steps to install the Flow CLI.
Starting the emulator by using Flow CLI also leverages CLI configuration file flow.json.
You can use the flow.json to specify the service account which will be reused between restarts.
Read more about CLI configuration here.
You can start the emulator with the Flow CLI:
flow emulator --initYou can start the emulator in your project context by running the above command
in the same directory as flow.json. This will configure the emulator with your
project's service account, meaning you can use it to sign and submit transactions.
Read more about the project and configuration here.
Docker builds for the emulator are automatically built and pushed to
gcr.io/flow-container-registry/emulator, tagged by commit and semantic version. You can also build the image locally.
docker run gcr.io/flow-container-registry/emulatorThe full list of environment variables can be found here.
You can pass any environment variable by using -e docker flag and pass the valid value.
Custom Configuration Example:
docker run -e FLOW_PORT=9001 -e FLOW_VERBOSE=true -e FLOW_SERVICEPUBLICKEY=<hex-encoded key> gcr.io/flow-container-registry/emulatorTo generate a service key, use the keys generate command in the Flow CLI.
flow keys generateRead contributing document.
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