This document discusses key metrics to monitor for Node.js applications, including event loop latency, garbage collection cycles and time, process memory usage, HTTP request and error rates, and correlating metrics across worker processes. It provides examples of metric thresholds and issues that could be detected, such as high garbage collection times indicating a problem or an event loop blocking issue leading to high latency.

1. Top Node.js Metrics to Watch
Stefan Thies

2. Agenda
- Development of node.js
performance monitoring agents
- Node.js key metrics

4. Metrics Aggregation
- pre-aggregation in monitoring agent
- N measures per minute -> sum, max, min, avg, rates, percentiles
- aggregation plans in Sematext backend (Java / Hadoop)
- 1 min, 5 min, 1 hour, 1 day, 1 week, 1 month
- fast queries over long periods of time and multiple dimensions
(e.g. filters for host, process/worker id)

5. Store & Forward
1)Buffer Metrics when the receiver is not reachable ...
2)Re-transmit metrics, stored in NeDB

6. 1 http.post(options, cb1)
3 http.post(options, cb2)
3 http.post(options, cb3)
4 http.post(options, cb4)
5 cb4 (err)
5 cb1
6 cb2
7 cb3
Java
Server
Threads, Thread Pool,
limited e.g. max 3
Node Client & Java Backend
async,
non-blocking
Main + Event
Loop Thread
HTTP 500
internal server error
Luke be nice to
Node.js Client

7. “A stupid guy called ‘Travis’, made DoS attacks!!!”
8 Minute Unit Tests for network/storage test cases
30 seconds :)

8. OS Metrics limited in node.js API
- Limited Memory info os.freemem(), os.totalmem()
- a few missing CPU metrics: os.cpus()
- No Disk stats in node API

9. How to Load the Monitoring Agent?
OK - for Devs, but Ops don’t like to touch source code ...
Node 4.x to the rescue!
Pre-loading modules with ‘-r’ / require

10. Garbage Collection
- Incremental marking and lazy sweeping
- marking ‘stop the world’
- Incremental GC cycles (scavenge)
- Full GC cycles
- What should be measured?
- Count of GC cycles
- Rate GC cycles / time
- Sum GC Time
- Released Memory (before GC - after GC)

11. How to get GC info?
Find GC options: node --v8-options | grep _gc
node --trace-gc --trace_gc_nvp lib/index.js
[7729:0x101804600] [I:0x101804600] 26 ms: pause=0.9 mutator=-1455940110228.4 gc=s
external=0.0 mark=0.0 sweep=0.00 sweepns=0.00 sweepos=0.00 sweepcode=0.00 sweepcell=0.00
sweepmap=0.00 evacuate=0.0 new_new=0.0 root_new=0.0 old_new=0.0 compaction_ptrs=0.0
intracompaction_ptrs=0.0 misc_compaction=0.0 weak_closure=0.0 inc_weak_closure=0.0
weakcollection_process=0.0 weakcollection_clear=0.0 weakcollection_abort=0.0
total_size_before=2360232 total_size_after=2257696 holes_size_before=32 holes_size_after=32
allocated=2360232 promoted=0 semi_space_copied=929376 nodes_died_in_new=7
nodes_copied_in_new=5 nodes_promoted=0 promotion_ratio=0.0% average_survival_ratio=90.1%
promotion_rate=0.0% semi_space_copy_rate=90.1% new_space_allocation_throughput=0
context_disposal_rate=0.0 steps_count=0 steps_took=0.0 scavenge_throughput=1180677

12. NPM modules for GC info
- gc-stats
- gc-profiler
- memwatch(-next)
- missing gc times
- + leak detection
- + heap diff
Native C++
modules V8
API / NAN 1.x
vs. NAN 2.x

14. NPM GC packages

15. GC Insights as part of Node.js API?

16. Examples for Node.js Metrics

17. - CPU Usage
- Memory Usage
- Disk
- I/O read/writes
- Space
- Process Metrics
- Application Metrics
- in-process monitor
Server, Process, Application Metrics

18. GC Metrics
GC cycles / min
< 50
GC Time
< 20 ms / min
Released Mem.
2 MB / cycle

19. Example - Monitoring Kibana 4.1 Node.js App
http://blog.sematext.com/2015/05/27/monitoring-kibana-4s-
node-js-app/
- 2.0 ruby server
- 3.0 HTML5 no server
- 4.0-4.2 Node Express
- > 4.3 Node Hapi.js
We run a managed
ELK Stack / Logging SaaS

20. GC cycles - out of control!
GC cycles / min: 45.000 (!)
GC Time: < 10 sec / min
???
OOM Kill

21. Taming GC ...
GC cycles / min: 100
GC Time: < 92 ms / min
--max-old-space-size=200
GC cycles / min: 45.000 (!)
GC Time: < 10 sec / min
Update to Node.js 4.2.x

22. Event Loop Latency
Avg. Latency < 0,5 ms

23. Event Loop Latency
EventLoop Latency < 0,5 ms 3 / 15 ms !!!
3 / 15 ms !!!

24. Don’t Block the Event Loop ...

25. Process Memory

26. Example - Process Memory
OOM Kill

27. Number of Workers

28. Number of Workers

29. Correlate Metrics for Different Workers

30. HTTP Metrics

31. HTTP Request and Error Rate

32. Error Breakdown

33. Get the Full Picture ...

34. Thank you!
www.npmjs.com/~megastef
www.npmjs.com/~sematext
@seti321 or @sematext