MaxGabriel

Monitoring a Yesod app with EKG

Monitoring is critical to a well-functioning production system. OS-level metrics like CPU load and RAM usage are a good start, but you'll eventually want to record application-level metrics like how long it's taking you to service each HTTP request, or how much time is spent in garbage collection. Once tracked, this data can be used by humans and machines (like monitoring systems) to gain insight into how your app is running.

In this post I'll show how you can use EKG, a popular Haskell metrics library, to add application-level metrics to your Yesod app.

A Brief Overview of EKG Metric Types

EKG allows reporting four different types of metrics from your app:

MaxGabriel

{
   "myapp":{
      "home_requests":{
         "type":"c",
         "val":0
      }
   },
   "ekg":{
      "server_timestamp_ms":{
         "type":"c",

MaxGabriel

Connecting to Redis from Yesod

This is a quick run-through of how I connected to Redis from a Yesod site (which used the default scaffolding). There isn't much specific to Redis here, so this information should apply to connecting to any database or service from Yesod.

Background: Basics of Hedis

First, a brief intro of the basics of Hedis:

{-# LANGUAGE OverloadedStrings #-}

MaxGabriel

Max@maximilians-mbp ~/D/i/C/S/H/5.0.2> pod spec lint --verbose --no-clean

    HZInMobi (5.0.2) - Analyzing on iOS 6.0 platform.
  Preparing

Analyzing dependencies

Fetching external sources
-> Fetching podspec for `HZInMobi` from `/Users/Max/Documents/iOS/CocoapodsSource/Specs/HZInMobi/5.0.2/HZInMobi.podspec`

MaxGabriel

tree
.
├── HZInMobi
├── Headers
├── Local Podspecs
│   └── HZInMobi.podspec.json
├── Manifest.lock
├── Pods.xcodeproj
│   ├── project.pbxproj
│   └── xcuserdata

MaxGabriel

Max@maximilians-mbp /t/C/S/H/5.0.2> pod spec lint --verbose --no-clean
WARN: Unresolved specs during Gem::Specification.reset:
      json (>= 1.7.7, ~> 1.7)
      minitest (~> 5.1)
WARN: Clearing out unresolved specs.
Please report a bug if this causes problems.

    HZInMobi (5.0.2) - Analyzing on iOS 6.0 platform.
  Preparing

MaxGabriel

while processing /Users/Max/Documents/iOS/ios-example-app/Chartboost.framework/Chartboost(CBTouchCallbackView.o):
warning: /Users/bob/Library/Developer/Xcode/DerivedData/Chartboost-dbglhohaluoolubfpjbzctgxcsdw/Build/Intermediates/PrecompiledHeaders/Chartboost-Prefix-gjlczopydjkegkafbxxfsnlbgwmm/Chartboost-Prefix.pch.pch: No such file or directory
while processing /Users/Max/Documents/iOS/ios-example-app/Chartboost.framework/Chartboost(CBTouchCallbackView.o):
warning: /Users/bob/Library/Developer/Xcode/DerivedData/Chartboost-dbglhohaluoolubfpjbzctgxcsdw/Build/Intermediates/PrecompiledHeaders/Chartboost-Prefix-gjlczopydjkegkafbxxfsnlbgwmm/Chartboost-Prefix.pch.pch: No object file for requested architecture
while processing /Users/Max/Documents/iOS/ios-example-app/Chartboost.framework/Chartboost(CBTouchCallbackView.o):
warning: Could not resolve external type c:objc(cs)UIView
while processing /Users/Max/Documents/iOS/ios-example-app/Chartboost.framework/Chartboost(CBTouchCallbackView.o):
warning: Could not resol

MaxGabriel

##########################################
#
# c.f. http://stackoverflow.com/questions/3520977/build-fat-static-library-device-simulator-using-xcode-and-sdk-4
#
# Version 2.7
#
# Latest Change:
# - Supports iPhone 5 / iPod Touch 5 (uses Apple's workaround to lipo bug)
# 
# Purpose:

MaxGabriel

<?xml version="1.0" encoding="utf-8" standalone="no"?>
<application xmlns="http://ns.adobe.com/air/application/19.0">

	<!-- Adobe AIR Application Descriptor File Template. Specifies parameters 
		for identifying, installing, and launching AIR applications. xmlns - The 
		Adobe AIR namespace: http://ns.adobe.com/air/application/3.1 The last segment 
		of the namespace specifies the version of the AIR runtime required for this 
		application to run. minimumPatchLevel - The minimum patch level of the AIR 
		runtime required to run the application. Optional. -->

MaxGabriel

    BOOL hz_chartboost_enabled(void) {
        return [HeyzapAds isNetworkInitialized:HZNetworkChartboost];
    }
    
    // Calling hz_fetch_chartboost_for_location recursively won't keep the `const char *` in memory
    // Since I want to call it recursively, I immediately convert to an `NSString *` in `hz_fetch_chartboost_for_location`
    void hz_fetch_chartboost_for_location_objc(NSString *location) {
        if (!hz_chartboost_enabled()) {
            NSLog(@"Chartboost not enabled; in 0.25 seconds");
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.25 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{