Instana Haskell Trace SDK  

Monitor your Haskell application with Instana! 🎉

Disclaimer

The Instana Haskell Trace SDK is a labor of love from some of our engineers and work on it is done in their spare time. Haskell is currently not a platform that we officialy support. The experience may differ from other programming languages and platforms that Instana actively supports (such as Java, .NET, Node.js, Python, Ruby, Go, PHP, ...). That said, the SDK is a fully functional piece of software, so don't let this disclaimer discourage you from using it. If you use Instana or consider using it and Haskell support is crucial for you, make sure to give us a ping and let's talk about it.

What The Haskell Trace SDK Is And What It Is Not

The Instana Haskell Trace SDK does not support automatic instrumentation/tracing in the way we support it in most other languages. Instead, the SDK enables you to create spans manually, much like the Instana Trace SDK for Java does. Besides offering a convenient API to create spans, the Haskell Trace SDK also takes care of establishing a connection to the Instana Agent and sending spans to the agent in an efficient way, that does not impede the performance of your production code.

Installation

NOTE: Currently, the instana-haskell-trace-sdk has not been published on Hackage yet, so adding it to your dependencies will not work yet. It will be published soon. Stay tuned!

To use the Instana Haskell Trace SDK in your application, add instana-haskell-trace-sdk to your dependencies (for example to the build-depends section of your cabal file).

Usage

Initialization

Before using the SDK, you need to initialize it once, usually during application startup.

import qualified Instana.SDK.SDK as InstanaSDK

main :: IO ()
main = do
  -- ... initialize things ...

  -- initialize Instana
  instana <- InstanaSDK.initInstana

  -- ... initialize more things

The value instana :: Instana.SDK.SDK.InstanaContext that is returned by InstanaSDK.initInstana is required for all further calls, that is, for creating spans that will be send to the agent. The SDK will try to connect to an agent (asynchronous, in a a separate thread) as soon as it receives the initInstana call.

The SDK can be configured via environment variables or directly in the code by passing configuration parameters to the initialization function, or both.

If you would like to pass configuration parameters programatically, use initConfiguredInstana instead of initInstana:

import qualified Instana.SDK.SDK as InstanaSDK

main :: IO ()
main = do

  -- Example snippet for using the Instana SDK and providing a configuration
  -- (agent host, port, ...) directly in code. You only need to specify the
  -- configuration values you are interested in and can omit everything else
  -- (see https://www.yesodweb.com/book/settings-types).
  let
    config =
      InstanaSDK.defaultConfig
        { InstanaSDK.agentHost = Just "127.0.0.1"
        , InstanaSDK.agentPort = Just 42699
        , InstanaSDK.forceTransmissionAfter = Just 1000
        , InstanaSDK.forceTransmissionStartingAt = Just 500
        , InstanaSDK.maxBufferedSpans = Just 1000
        }
  instana <- InstanaSDK.initConfiguredInstana config

For configuration parameters that are omitted when creating the config record or are set to Nothing, the SDK will fall back to environment variables (see below) and then to default values.

There are also bracket-style variants of the initialization function, called withInstana and withConfiguredInstana:

import qualified Instana.SDK.SDK as InstanaSDK

main :: IO ()
main = do
  InstanaSDK.withInstana runApp

runApp :: InstanaContext -> IO ()
runApp instana = do
  -- do your thing here :-)

or, with bracket style and a configuration record:

import qualified Instana.SDK.SDK as InstanaSDK

main :: IO ()
main = do
  let
    config =
      InstanaSDK.defaultConfig
        { InstanaSDK.agentHost = Just "127.0.0.1"
        , InstanaSDK.agentPort = Just 42699
        , InstanaSDK.forceTransmissionAfter = Just 1000
        , InstanaSDK.forceTransmissionStartingAt = Just 500
        , InstanaSDK.maxBufferedSpans = Just 1000
        }

  InstanaSDK.withConfiguredInstana config runApp

runApp :: InstanaContext -> IO ()
runApp instana = do
  -- do your thing here :-)

Creating Spans

Bracket Style (High Level API)

All functions starting with with accept (among other parameters) an IO action. The SDK will start a span before, then execute the given IO action and complete the span afterwards. Using this style is recommended over the low level API that requires you to start and complete spans yourself.

• withRootEntry: Creates an entry span that is the root of a trace (it has no parent span).
• withEntry: Creates an entry span that has a parent span.
• withExit: Creates an exit span. This can only be called inside a withRootEntry or an withEntry call, as an exit span needs an entry span as its parent.

Low Level API/Explicit Start And Complete

• startRootEntry: Starts an entry span that is the beginning of a trace (has no parent span). You will need to call completeEntry at some point.
• startEntry: Starts an entry span. You will need to call completeEntry at some point.
• startExit: Starts an exit span. You need to call completeExit/completeExitWithData at some point with the partial exit span value that is returned by this function.
• completeEntry: Finalizes an entry span. This will put the span into the SDK's span buffer for transmission to the Instana agent.
• completeExit: Finalizes an exit span. This will put the span into the SDK's span buffer for transmission to the Instana agent.

Configuration Via Environment Variables

Instead of configuring the SDK programatically, as seen above, it can also be configured via environment variables:

• INSTANA_AGENT_HOST: The IP or the host of the Instana agent to connect to. Default: 127.0.0.1.
• INSTANA_AGENT_PORT: The port of the Instana agent to connect to. Default: 42699.
• INSTANA_AGENT_NAME: When establishing a connection to the Instana agent, the SDK validates the Instana agent's Server HTTP response header. Should you have changed the Server name on the agent side, you can use this environment variable to provide the name to match that header against.
• INSTANA_FORCE_TRANSMISSION_STARTING_AFTER: Spans are usually buffered before being transmitted to the agent. This setting forces the transmission of all buffered spans after the given amount of milliseconds. Default: 1000.
• INSTANA_FORCE_TRANSMISSION_STARTING_AT: This setting forces the transmission of all buffered spans when the given number of spans has been buffered.
• INSTANA_MAX_BUFFERED_SPANS: Limits the number of spans to buffer. When the limit is reached, spans will be dropped. This setting is a safe guard against memory leaks from buffering excessive amounts of spans. It must be larger than INSTANA_FORCE_TRANSMISSION_STARTING_AT.
• INSTANA_LOG_LEVEL: See section "Configure Debug Logging".
• INSTANA_LOG_LEVEL_STDOUT: See section "Configure Debug Logging".
• INSTANA_OVERRIDE_HSLOGGER_ROOT_HANDLER: See section "Configure Debug Logging".

Configure Debug Logging

If required, the Instana Haskell SDK can produce logs via hslogger. Under normal circumstances, the SDK does not emit any log output at all. It will only output log messages when logging is explicitly enabled via certain environment variables. This can be useful to troubleshoot tracing in production settings or during development.

Logging Related Environment Variables

• INSTANA_LOG_LEVEL: Sets the log level for the SDK's log file. The log file will be written to the system's temporary directory (in particular, whatever System.Directory.getTemporaryDirectory returns) as instana-haskell-sdk.{pid}.log.
• INSTANA_LOG_LEVEL_STDOUT: Sets the level for emitting log messages to stdout.
• INSTANA_OVERRIDE_HSLOGGER_ROOT_HANDLER: Controls whether the SDK sets an hslogger at the root logger level, see below.

When To Set INSTANA_OVERRIDE_HSLOGGER_ROOT_HANDLER

Setting up hslogger correctly inside a library like the Instana Haskell SDK (as opposed to an application which has full control) can be tricky. For the Instana Haskell SDK to be able to correctly configure hslogger, it is important to know whether the app in question (or some part of it) already uses hslogger. In particular, does some part of the code set a handler on hslogger's root logger? Is a call like the following executed somewhere in the application?

import System.Log.Logger (rootLoggerName, setHandlers, updateGlobalLogger)

updateGlobalLogger rootLoggerName $ setHandlers [...]

If this is the case, you can simply use INSTANA_LOG_LEVEL (or INSTANA_LOG_LEVEL_STDOUT) without further configuration. If the app in question does not use hslogger, that is, if no setHandler call on rootLoggerName is executed, you should also set INSTANA_OVERRIDE_HSLOGGER_ROOT_HANDLER to a non-empty string (for example, INSTANA_OVERRIDE_HSLOGGER_ROOT_HANDLER=true).

Troubleshooting Tracing In Production

If your app already uses hslogger, use:

• INSTANA_LOG_LEVEL=DEBUG

Otherwise, use:

• INSTANA_LOG_LEVEL=DEBUG INSTANA_OVERRIDE_HSLOGGER_ROOT_HANDLER=true

Development

During development (that is, when working on the Instana Haskell SDK), use either

• INSTANA_LOG_LEVEL_STDOUT=DEBUG

or

• INSTANA_LOG_LEVEL_STDOUT=DEBUG
• INSTANA_OVERRIDE_HSLOGGER_ROOT_HANDLER=true

depending on whether the application already uses and configures hslogger. The application example-app that is contained in the Instana Haskell SDK's repo configures hslogger, so simply using INSTANA_LOG_LEVEL_STDOUT=DEBUG is correct.

Contributing

See CONTRIBUTING.md.