Eclair

Eclair is an implementation of a full Lightning Network node, written in Scala and maintained by ACINQ. It runs on the Java Virtual Machine (JVM) and follows the Lightning specification (the BOLTs). ACINQ uses Eclair to power its own production infrastructure — including the node backing its widely used mobile wallet — and the same software is available as open source under the Apache License 2.0, meaning the code that runs one of the network's largest routing operations is available for anyone to read, audit, and deploy.

Design and intended use

Eclair is built primarily for server-side deployment rather than for a phone or a low-power single-board computer. The JVM foundation brings the strengths of that ecosystem — mature concurrency via an actor-model architecture, strong typing, battle-tested tooling — and makes Eclair a natural fit for operators who already run Java or Scala infrastructure and want a node implementation designed to handle routing and channel management at scale. The trade-off is resource appetite: a JVM process is heavier than a lean C daemon, which is why Eclair appears more often in server racks than on Raspberry Pis. Because ACINQ operates major routing infrastructure on this exact codebase, Eclair's development is unusually grounded in production reality — features and fixes tend to reflect problems actually encountered while moving real payments at volume.

Running Eclair

Like other Lightning implementations, Eclair connects to a Bitcoin Core backend to watch the chain, verify channel funding, and broadcast on-chain transactions — the Lightning layer inherits its security from the Bitcoin node beneath it. The project ships a Docker image for containerized deployment and supports the standard networks (mainnet, testnet, regtest) for development and staging. A plugin system allows operators to extend behavior without modifying the core, and configuration exposes the levers a routing operator cares about: channel policies, fee settings, and relay parameters.

APIs and operational security

Eclair exposes an HTTP JSON API for opening channels, sending and receiving payments, and querying node state. The project documentation stresses that this API must never be exposed directly to the public internet, since it controls funds — a warning that generalizes to every Lightning node management interface, whatever the implementation. A Lightning node is a hot wallet by construction: it holds signing keys online because the protocol requires it, so the management surface deserves the same treatment as the keys themselves — local-network or VPN access only, strong authentication, and nothing you would not want an attacker to reach. Keep serious funds on-chain in self-custody; fund channels with what the node actually needs.

Operating a routing node

Because Eclair targets the server-side niche, its typical operator is running a routing business, however small: committing capital to channels and earning fees for forwarding payments. That job is mostly liquidity management — choosing peers with real payment demand, sizing channels so they are useful in both directions, setting fee policy that reflects the value of your liquidity, and rebalancing when flows push channels to one side. It rewards the same operational temperament as running miners: monitoring, capacity planning, and patience with unglamorous maintenance. Start small, measure actual forwarding activity before scaling capital, and remember that a routing node's uptime is its reputation.

Eclair is one of several specification-compliant implementations, and the diversity is a strength — independent codebases in different languages mean a bug in one is unlikely to be shared by the others. We describe each neutrally so node runners can choose what matches their environment and skills. ACINQ also builds the mobile-facing side of this stack — see our entries on Phoenix Wallet, Core Lightning (CLN), and LND (Lightning Network Daemon) for the rest of the landscape.