Perlbal 1.72

Perlbal is a single-threaded event-based server supporting HTTP load balancing, web serving, and a mix of the two.
One of the defining things about Perlbal is that almost everything can be configured or reconfigured on the fly without needing to restart the software.
Also, a basic configuration file containing a management port will enables the user to easily perform operations on a running instance of Perlbal.
Main features:
Web Server
- Listen on a port, share from a directory
- Directory indexing
- Byte range support (clients can resume downloads)
- Can have directory index requests fall back to index file list
- Persistent client connections (configurable)
- Almost all1 disk operations are done asynchronously as to not stall the event loop
- Configurable support for storing files (PUT, DELETE support)
Reverse Proxy
- Maintains pool of connected backend connections to reduce turnover
- Gets list of nodes either from asynchronously monitored node file, or from in-server pool objects which you can add/remove nodes from using the management interface.
- Intelligent load balancing based on what backend connections are free for a new request. No unreliable "weighting" numbers required.
- Can verify (using a quick OPTIONS request) that a backend connection is talking to a webserver and not just the kernels listen queue before sending client requests at it. Lower latency for the client.
- Has a high priority queue for sending requests through to backends quickly
- Can allow X-Forwarded-For (and similar) headers from client based on client IP
- Configurable header management before sending request to backend
- Internal redirection to file or URL(s)
- Persistent client connections (configurable)
- Persistent backend connections (shared by multiple clients; no "backend waste")
Performance
- Event-based using epoll or kqueue to avoid the scalability problems of not-so-modern systems
- HTTP Header processing (optionally) done in C with Perlbal::XS::HTTPHeaders for maximum performance
- 100% asynchronous in all the recommended use cases
- Lightweight
- Great performance "out-of-the-box" (for both small and large sites)
Statistics and Monitoring
The management interface provides extremely detailed and powerful statistics in addition to runtime configuration. For example:
- CPU usage (user, system)
- Total requests served across all services
- Requests service by individual backends
- Perlbal uptime
- All connected sockets (and tons of info about each)
- Outstanding connections to backends
- Backends that have recently failed verification
- Pending backend connections by service
- Total of all socket states by socket type
- Size (in seconds and number of connections) of all queues
- State of reproxy engine (queued requests, outstanding requests, backends)
- Loaded plugins per service
Plugins (Extensibility)
Perlbal supports the concept of having per-service (and global) plugins that can override many parts of request handling and behavior.