network-wait

A lightweight Haskell library for waiting on networked services to become available. This is useful if you are e.g. building a web application which relies on a database server to be available, but which may not be immediately available on application startup.

Example

All functions provided by this library work with retry policies from Control.Retry which provide good control over the retry behaviour. To wait for a PostgreSQL server to become available on the same machine:

import Control.Retry
import Network.Wait

main :: IO ()
main = do
    waitTcp retryPolicyDefault "localhost" "5432"
    putStrLn "Yay, the server is available!"

The haddock documentation for this library contains more examples.

See also

• wait-for is a popular shell script with the same objectives as this library.
• The port-utils package has some functions for waiting on TCP servers to become available, with a fixed timeout.