Utilities

The following utilities may be useful when developing Surge applications.

MDC Logging

• The Mapped Diagnostic Context(MDC) allows us to put context to all log statements for a single thread.
• It is exposed via org.slf4j.MDC if you are using slf4j but other logging systems (such as log4j and logback) have similar concepts that slf4j wraps.

MDC Propagation Across Futures

• To propagate MDC across Futures, first we need to import the mdcExecutionContext which copies the MDC to any new thread that is being used giving us multi-thread MDC logging.

  import surge.internal.utils.MdcExecutionContext.mdcExecutionContext
  

  By default, mdcExecutionContext wraps the default global ExecutionContext and adds MDC propagation support to it. But if you want to use your own ExecutionContext, then you can do so by passing it in as an argument to the DiagnosticContextFuturePropagation constructor:

    implicit lazy val mdcExecutionContext: ExecutionContext = new DiagnosticContextFuturePropagation(yourOwnExecutionContext)
  

  Note: DiagnosticContextFuturePropagation is exposed via surge.internal.utils.DiagnosticContextFuturePropagation

• Next, we need to put the context in our log statements:

  MDC.put("requestId", UUID.randomUUID().toString())
  

  That’s all. Using these two simple steps, we can propagate our MDC from the caller thread to the execution thread.