EPF4: UPDATE 8

## 'STARTING AND RESTARTING LODESTAR'

### 1. How is Lodestar started ?

Lodestar is started using the beaconHandler.

The explicit command responsible for this can be found [here](https://github.com/atkinsonholly/lodestar/blob/unstable/packages/cli/src/cmds/beacon/index.ts):
.

The most important function responsible for this implementation in that file can be found [here](https://github.com/atkinsonholly/lodestar/blob/unstable/packages/cli/src/cmds/beacon/handler.ts):

There are three functions in that file:
* beaconHandler()
* beaconHandlerInit()
* InitLogger()

The most function we are concerned with is the beaconHandler().
Reason: It incorporates the other two functions and also contains the code for starting and stopping Lodestar.

The **beaconHandler** does the following:
* Sets time-interval constants for periodic handling of ssz objects:
`const DEFAULT_RETENTION_SSZ_OBJECTS_HOURS = 154 * 24;`
`const HOURS_TO_MS = 3600 * 1000;`

* **Runs the beacon node as a whole:**
`export async function beaconHandler(args: BeaconArgs & GlobalArgs): Promise<void> {}`

* Initializes the beacon handler:
`const {config, options, beaconPaths, network, version, commit, peerId, logger} = await beaconHandlerInit(args); `
* imports`beaconHandlerInit` for initializing the node;
* this function ensures that process by setting up the variables within it {config, options, etc} responsible for successfully initializing the beacon node

* Initializes directories:
`
mkdir(beaconPaths.dataDir);
mkdir(beaconPaths.beaconDir);
mkdir(beaconPaths.dbDir);
`
* dataDir - general data fies
* beaconDir - specific to beacon files
* dbDir - beacon database(metadata about beacon files)

* Aborts network operations:
`
const abortController = new AbortController();
`

* Logs information about the following variables on the terminal:
`
logger.info("Lodestar", {network, version, commit});
`

* Callback for beacon to request forced exit, for e.g. in case of irrecoverable forkchoice errors. This signal is typically sent when the user presses **Ctrl + C** on the terminal:
`
const processShutdownCallback: ProcessShutdownCallback = (err) => {
logger.error("Process shutdown requested", {}, err);
process.kill(process.pid, "SIGINT");
};
`

* Logs information about preset network configs:
`
if (ACTIVE_PRESET === PresetName.minimal) logger.info("ACTIVE_PRESET == minimal preset");
`

* Additional metrics registries(sets up the network's metric data):
`
const metricsRegistries: Registry[] = [];
let networkRegistry: Registry | undefined;
if (options.metrics.enabled) {
networkRegistry = new Registry();
metricsRegistries.push(networkRegistry);
}
`

* Creates a new beacon database with the variables in the `BeaconDb` object. Logs the information:
`const db = new BeaconDb(config, await LevelDbController.create(options.db, {metrics: null, logger}));
logger.info("Connected to LevelDB database", {path: options.db.name});
`

* BeaconNode setup:

* Sets up the beacon state with `initBeaconState`. It returns anchorState and wsCheckpoint:
`
try {
const {anchorState, wsCheckpoint} = await initBeaconState(
options,
args,
config,
db,
logger,
abortController.signal
);
`
* where anchorState is the reference point for validators.
* wsCheckpoint is the backup of the beacon state which validators can use to sync asap during outage.

* Create beacon chain config object for initiliazing the beacon chain:
`
const beaconConfig = createBeaconConfig(config, anchorState.genesisValidatorsRoot);
`

* Initialize the beacon node using `BeaconNode.init`:
`
const node = await BeaconNode.init({
opts: options,
config: beaconConfig,
db,
logger,
processShutdownCallback,
peerId,
peerStoreDir: beaconPaths.peerStoreDir,
anchorState,
wsCheckpoint,
metricsRegistries,
});
`

* Dev debug option to have access to the BN instance
`
if (args.attachToGlobalThis) {
(globalThis as unknown as {bn: BeaconNode}).bn = node;
}
`

* Prune invalid SSZ objects (old files) every interval
`
const {persistInvalidSszObjectsDir} = args;
const pruneInvalidSSZObjectsInterval = persistInvalidSszObjectsDir
? setInterval(() => {
try {
pruneOldFilesInDir(
persistInvalidSszObjectsDir,
(args.persistInvalidSszObjectsRetentionHours ?? DEFAULT_RETENTION_SSZ_OBJECTS_HOURS) * HOURS_TO_MS
);
} catch (e) {
logger.warn("Error pruning invalid SSZ objects", {persistInvalidSszObjectsDir}, e as Error);
}
// Run every ~1 hour
}, HOURS_TO_MS)
: null;
`

* Intercept SIGINT signal, to perform final ops before exiting:
`
onGracefulShutdown(async () => {
if (args.persistNetworkIdentity) {
try {
const networkIdentity = await node.network.getNetworkIdentity();
const enrPath = path.join(beaconPaths.beaconDir, "enr");
writeFile600Perm(enrPath, networkIdentity.enr);
} catch (e) {
logger.warn("Unable to persist enr", {}, e as Error);
}
}
abortController.abort();
`
* performs cleanup and finalization tasks
* persists the network identity
* aborts ongoing operations

* Stops pruning ssz objects:
`
if (pruneInvalidSSZObjectsInterval !== null) {
clearInterval(pruneInvalidSSZObjectsInterval);
}
}, logger.info.bind(logger));
`

* Ensures the beacon node and database are closed gracefully when an abort signal is received:
`
abortController.signal.addEventListener(
"abort",
async () => {
try {
await node.close();
logger.debug("Beacon node closed");resolved
process.exit(0);
} catch (e) {
logger.error("Error closing beacon node", {}, e as Error);
await db.close();
process.exit(1);
}
},
{once: true}
);
} catch (e) {
await db.close();
if (e instanceof ErrorAborted) {
logger.info(e.message);
} else {
throw e;
}
}
`

**WIL:**

* The client starts the network with the beacon handler.
* The client can be stopped with onGracefulShutdown && abortController for a reset
* The reset involves a dependency(import files) for checking for if a new genesis available.

### 2. How to pause Lodestar so a reset can be implemented
* onGracefulShutdown()
* A callback function that is called when a signal is received (usually Ctrl + C).
* In our case, the signal will be a new genesis available
* Once a new genesis is confirmed to be availabe, a function very similar to onGracefulShutdown() will be called
* the function can be called gracefulSuspension() to indicate that the network operations are temporarily being suspended or it can be explicitly defined that only certain activities like transactions are shutdown, so that the rest of the network can move to a new genesis.
* Probably not neccessary to persist the network identity or ENR in this case because a new one will be generated with a new genesis.
* Should modify the `abortController()` since we do not explicitly want to close node operations.
* This means canceling out `node.close()` and keepind `db.close()`b this means that while the node operations are still active, the database activities will be shutdown.

### Links
* [beacon-node database](https://github.com/atkinsonholly/lodestar/blob/unstable/packages/beacon-node/src/db/beacon.ts#L89) that will be closed.