How Geth starts its server

// Backend interface provides the common API services (that are provided by
// both full and light clients) with access to necessary functions.
type Backend interface {
	// General Ethereum API
	SyncProgress() ethereum.SyncProgress

	SuggestGasTipCap(ctx context.Context) (*big.Int, error)
	FeeHistory(ctx context.Context, blockCount uint64, lastBlock rpc.BlockNumber, rewardPercentiles []float64) (*big.Int, [][]*big.Int, []*big.Int, []float64, error)
	ChainDb() ethdb.Database
	AccountManager() *accounts.Manager
	ExtRPCEnabled() bool
	RPCGasCap() uint64            // global gas cap for eth_call over rpc: DoS protection
	RPCEVMTimeout() time.Duration // global timeout for eth_call over rpc: DoS protection
	RPCTxFeeCap() float64         // global tx fee cap for all transaction related APIs
	UnprotectedAllowed() bool     // allows only for EIP155 transactions.

	// Blockchain API
	SetHead(number uint64)
	HeaderByNumber(ctx context.Context, number rpc.BlockNumber) (*types.Header, error)
	HeaderByHash(ctx context.Context, hash common.Hash) (*types.Header, error)
	HeaderByNumberOrHash(ctx context.Context, blockNrOrHash rpc.BlockNumberOrHash) (*types.Header, error)
	CurrentHeader() *types.Header
	CurrentBlock() *types.Header
	BlockByNumber(ctx context.Context, number rpc.BlockNumber) (*types.Block, error)
	BlockByHash(ctx context.Context, hash common.Hash) (*types.Block, error)
	BlockByNumberOrHash(ctx context.Context, blockNrOrHash rpc.BlockNumberOrHash) (*types.Block, error)
	StateAndHeaderByNumber(ctx context.Context, number rpc.BlockNumber) (*state.StateDB, *types.Header, error)
	StateAndHeaderByNumberOrHash(ctx context.Context, blockNrOrHash rpc.BlockNumberOrHash) (*state.StateDB, *types.Header, error)
	PendingBlockAndReceipts() (*types.Block, types.Receipts)
	GetReceipts(ctx context.Context, hash common.Hash) (types.Receipts, error)
	GetTd(ctx context.Context, hash common.Hash) *big.Int
	GetEVM(ctx context.Context, msg *core.Message, state *state.StateDB, header *types.Header, vmConfig *vm.Config, blockCtx *vm.BlockContext) (*vm.EVM, func() error)
	SubscribeChainEvent(ch chan<- core.ChainEvent) event.Subscription
	SubscribeChainHeadEvent(ch chan<- core.ChainHeadEvent) event.Subscription
	SubscribeChainSideEvent(ch chan<- core.ChainSideEvent) event.Subscription

	// Transaction pool API
	SendTx(ctx context.Context, signedTx *types.Transaction) error
	GetTransaction(ctx context.Context, txHash common.Hash) (*types.Transaction, common.Hash, uint64, uint64, error)
	GetPoolTransactions() (types.Transactions, error)
	GetPoolTransaction(txHash common.Hash) *types.Transaction
	GetPoolNonce(ctx context.Context, addr common.Address) (uint64, error)
	Stats() (pending int, queued int)
	TxPoolContent() (map[common.Address][]*types.Transaction, map[common.Address][]*types.Transaction)
	TxPoolContentFrom(addr common.Address) ([]*types.Transaction, []*types.Transaction)
	SubscribeNewTxsEvent(chan<- core.NewTxsEvent) event.Subscription

	ChainConfig() *params.ChainConfig
	Engine() consensus.Engine

	// This is copied from filters.Backend
	// eth/filters needs to be initialized from this backend type, so methods needed by
	// it must also be included here.
	GetBody(ctx context.Context, hash common.Hash, number rpc.BlockNumber) (*types.Body, error)
	GetLogs(ctx context.Context, blockHash common.Hash, number uint64) ([][]*types.Log, error)
	SubscribeRemovedLogsEvent(ch chan<- core.RemovedLogsEvent) event.Subscription
	SubscribeLogsEvent(ch chan<- []*types.Log) event.Subscription
	SubscribePendingLogsEvent(ch chan<- []*types.Log) event.Subscription
	BloomStatus() (uint64, uint64)
	ServiceFilter(ctx context.Context, session *bloombits.MatcherSession)
}

type SyncProgress struct {
	StartingBlock uint64 // Block number where sync began
	CurrentBlock  uint64 // Current block number where sync is at
	HighestBlock  uint64 // Highest alleged block number in the chain

	// "fast sync" fields. These used to be sent by geth, but are no longer used
	// since version v1.10.
	PulledStates uint64 // Number of state trie entries already downloaded
	KnownStates  uint64 // Total number of state trie entries known about

	// "snap sync" fields.
	SyncedAccounts      uint64 // Number of accounts downloaded
	SyncedAccountBytes  uint64 // Number of account trie bytes persisted to disk
	SyncedBytecodes     uint64 // Number of bytecodes downloaded
	SyncedBytecodeBytes uint64 // Number of bytecode bytes downloaded
	SyncedStorage       uint64 // Number of storage slots downloaded
	SyncedStorageBytes  uint64 // Number of storage trie bytes persisted to disk

	HealedTrienodes     uint64 // Number of state trie nodes downloaded
	HealedTrienodeBytes uint64 // Number of state trie bytes persisted to disk
	HealedBytecodes     uint64 // Number of bytecodes downloaded
	HealedBytecodeBytes uint64 // Number of bytecodes persisted to disk

	HealingTrienodes uint64 // Number of state trie nodes pending
	HealingBytecode  uint64 // Number of bytecodes pending
}

// Node is a container on which services can be registered.
type Node struct {
	eventmux      *event.TypeMux
	config        *Config
	accman        *accounts.Manager
	log           log.Logger
	keyDir        string        // key store directory
	keyDirTemp    bool          // If true, key directory will be removed by Stop
	dirLock       *flock.Flock  // prevents concurrent use of instance directory
	stop          chan struct{} // Channel to wait for termination notifications
	server        *p2p.Server   // Currently running P2P networking layer
	startStopLock sync.Mutex    // Start/Stop are protected by an additional lock
	state         int           // Tracks state of node lifecycle

	lock          sync.Mutex
	lifecycles    []Lifecycle // All registered backends, services, and auxiliary services that have a lifecycle
	rpcAPIs       []rpc.API   // List of APIs currently provided by the node
	http          *httpServer //
	ws            *httpServer //
	httpAuth      *httpServer //
	wsAuth        *httpServer //
	ipc           *ipcServer  // Stores information about the ipc http server
	inprocHandler *rpc.Server // In-process RPC request handler to process the API requests

	databases map[*closeTrackingDB]struct{} // All open databases
}

// Ethereum implements the Ethereum full node service.
type Ethereum struct {
	config *ethconfig.Config

	// Handlers
	txPool *txpool.TxPool

	blockchain         *core.BlockChain
	handler            *handler
	ethDialCandidates  enode.Iterator
	snapDialCandidates enode.Iterator
	merger             *consensus.Merger

	// DB interfaces
	chainDb ethdb.Database // Block chain database

	eventMux       *event.TypeMux
	engine         consensus.Engine
	accountManager *accounts.Manager

	bloomRequests     chan chan *bloombits.Retrieval // Channel receiving bloom data retrieval requests
	bloomIndexer      *core.ChainIndexer             // Bloom indexer operating during block imports
	closeBloomHandler chan struct{}

	APIBackend *EthAPIBackend

	miner     *miner.Miner
	gasPrice  *big.Int
	etherbase common.Address

	networkID     uint64
	netRPCService *ethapi.NetAPI

	p2pServer *p2p.Server

	lock sync.RWMutex // Protects the variadic fields (e.g. gas price and etherbase)

	shutdownTracker *shutdowncheck.ShutdownTracker // Tracks if and when the node has shutdown ungracefully
}