liftbridge-io/liftbridge: Lightweight, fault-tolerant message streams.

Liftbridge Logo


Liftbridge provides lightweight, fault-tolerant message streams by implementing
a durable stream augmentation for the NATS messaging system.
It extends NATS with a Kafka-like publish-subscribe log API that is highly
available and horizontally scalable. Use Liftbridge as a simpler and lighter
alternative to systems like Kafka and Pulsar or use it to add streaming
semantics to an existing NATS deployment.

See the introduction
post on Liftbridge and this post
for more context and some of the inspiration behind it.

Table of Contents

Key Features

  • Log-based API for NATS
  • Replicated for fault-tolerance
  • Horizontally scalable
  • Wildcard subscription support
  • At-least-once delivery support
  • Message key-value support
  • Log compaction by key
  • Single static binary (~16MB)
  • Designed to be high-throughput (more on this to come)
  • Supremely simple


What is Liftbridge?

Liftbridge is a server that implements a durable, replicated message log for
NATS. Clients create a named stream
which is attached to a NATS subject. The stream then records messages on that
subject to a replicated write-ahead log. Multiple consumers can read back
from the same stream, and multiple streams can be attached to the same
subject. Liftbridge provides a Kafka-like API in front of NATS.

Why was it created?

Liftbridge was designed to bridge the gap between sophisticated log-based
messaging systems like Apacha Kafka and Apache Pulsar and simpler, cloud-native
systems. There is no ZooKeeper or other unwieldy dependencies, no JVM, no
complicated API, and client libraries are just gRPC. More
importantly, Liftbridge aims to extend NATS with a durable, at-least-once
delivery mechanism that upholds the NATS tenets of simplicity, performance, and
scalability. Unlike NATS
, it uses the core
NATS protocol with optional extensions. This means it can be added to an
existing NATS deployment to provide message durability with no code changes.

Why not NATS Streaming?

NATS Streaming provides a
similar log-based messaging solution. However, it is an entirely separate
protocol built on top of NATS. NATS is simply the transport for NATS Streaming.
This means there is no “cross-talk” between messages published to NATS and
messages published to NATS Streaming.

Liftbridge was built to augment NATS with durability rather than providing a
completely separate system. NATS Streaming also provides a broader set of
features such as durable subscriptions, queue groups, pluggable storage
backends, and multiple fault-tolerance modes. Liftbridge aims to have a small
API surface area.

The key features that differentiate Liftbridge are the shared message namespace,
wildcards, log compaction, and horizontal scalability. NATS Streaming replicates
channels to the entire cluster through a single Raft group. Liftbridge allows
replicating to a subset of the cluster, and each stream is replicated
independently. This allows the cluster to scale horizontally.

How does it scale?

Liftbridge scales horizontally by adding more brokers to the cluster and
creating more streams which are distributed among the cluster. In effect, this
splits out message routing from storage and consumption, which allows
Liftbridge to scale independently and eschew subject partitioning.
Alternatively, streams can join a load-balance group, which effectively load
balances a NATS subject among the streams in the group without affecting
delivery to other streams.

What about HA?

High availability is achieved by replicating the streams. When a stream is
created, the client specifies a replicationFactor, which determines the
number of brokers to replicate the stream. Each stream has a leader who is
responsible for handling reads and writes. Followers then replicate the log
from the leader. If the leader fails, one of the followers can set up to
replace it. The replication protocol closely resembles that of Kafka, so there
is much more nuance to avoid data consistency problems. See the
replication protocol documentation for
more details.

What about performance?

Benchmarks soon to come…

Is it production-ready?

No, this project is early and still evolving.


$ go get

Quick Start

Liftbridge currently relies on an externally running
NATS server. By default, it will connect
to a NATS server running on localhost. The --nats-servers flag allows
configuring the NATS server(s) to connect to.

Also note that Liftbridge is clustered by default and relies on Raft for
coordination. This means a cluster of three or more servers is normally run
for high availability, and Raft manages electing a leader. A single server is
actually a cluster of size 1. For safety purposes, the server cannot elect
itself as leader without using the --raft-bootstrap-seed flag, which will
indicate to the server to elect itself as leader. This will start a single
server that can begin handling requests. Use this flag with caution as it should
only be set on one server when bootstrapping a cluster.

$ liftbridge --raft-bootstrap-seed
INFO[2019-06-28 01:12:45] Server ID:        OoVo48CniWsjYzlgGtKLB6
INFO[2019-06-28 01:12:45] Namespace:        liftbridge-default
INFO[2019-06-28 01:12:45] Retention Policy: [Age: 1 week, Compact: false]
INFO[2019-06-28 01:12:45] Starting server on :9292...
INFO[2019-06-28 01:12:46] Server became metadata leader, performing leader promotion actions

Once a leader has been elected, other servers will automatically join the cluster.
We set the --data-dir and --port flags to avoid clobbering the first server.

$ liftbridge --data-dir /tmp/liftbridge/server-2 --port=9293
INFO[2019-06-28 01:15:21] Server ID:        zsQToZyzR8WZfAUBiHSFvX
INFO[2019-06-28 01:15:21] Namespace:        liftbridge-default
INFO[2019-06-28 01:15:21] Retention Policy: [Age: 1 week, Compact: false]
INFO[2019-06-28 01:15:21] Starting server on :9293...

We can also bootstrap a cluster by providing the explicit cluster configuration.
To do this, we provide the IDs of the participating peers in the cluster using the
--raft-bootstrap-peers flag. Raft will then handle electing a leader.

$ liftbridge --raft-bootstrap-peers server-2,server-3


In addition to the command-line flags, Liftbridge can be fully configured using
a configuration file which is passed in using the --config flag.

$ liftbridge --config liftbridge.conf

An example configuration file is shown below.

listen: localhost:9293
data.dir: /tmp/liftbridge/server-2
log.level: debug

# Define NATS cluster to connect to.
nats {
    servers: ["nats://localhost:4300", "nats://localhost:4301"]

# Specify message log settings.
log {
    retention.max.age: "24h"

# Specify cluster settings.
clustering { server-2
    raft.logging: true
    raft.bootstrap.seed: true
    replica.max.lag.time: "20s"

See the configuration documentation for full
details on server configuration.

Client Libraries

Currently, there is only a high-level
Go client library available.
However, Liftbridge uses gRPC for its client API, so client libraries can
be generated quite easily using the
Liftbridge protobuf definitions.



  • Derek Collison and NATS team for
    building NATS and NATS Streaming and providing lots of inspiration.
  • Travis Jeffery for building
    Jocko, a Go implementation of
    Kafka. The Liftbridge log implementation builds heavily upon the commit log
    from Jocko.
  • Apache Kafka for inspiring large parts of the
    design, particularly around replication.