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Scribe is a server for aggregating streaming log data. It is designed to scale to a very large number of nodes and be robust to network and node failures. There is a scribe server running on every node in the system, configured to aggregate messages and send them to a central scribe server (or servers) in larger groups. If the central scribe server isn’t available the local scribe server writes the messages to a file on local disk and sends them when the central server recovers. The central scribe server(s) can write the messages to the files that are their final destination, typically on an nfs filer or a distributed filesystem, or send them to another layer of scribe servers.
Scribe is unique in that clients log entries consisting of two strings, a category and a message. The category is a high level description of the intended destination of the message and can have a specific configuration in the scribe server, which allows data stores to be moved by changing the scribe configuration instead of client code. The server also allows for configurations based on category prefix, and a default configuration that can insert the category name in the file path. Flexibility and extensibility is provided through the “store” abstraction. Stores are loaded dynamically based on a configuration file, and can be changed at runtime without stopping the server. Stores are implemented as a class hierarchy, and stores can contain other stores. This allows a user to chain features together in different orders and combinations by changing only the configuration.
Scribe is implemented as a thrift service using the non-blocking C++ server. The installation at facebook runs on thousands of machines and reliably delivers tens of billions of messages a day.