QUestions We'll Answer
- What's the difference between
- A smoke test
- A load test
- A stress test
- A spike test
- When should I load test?
- How can I match my load test with (anticipated) reality for more useful results?
- What bottlenecks should I be looking for when testing?
- What tools can I use to throw load at my site?
- How can I use one to test my application?
Questions we won't answer
- How do I use {JMeter|Gatling|Molotov}?
- How can I set up clustered load testing?
- How can I simulate far-end users?
- Slow connections tie up server/load balancer resources for longer
- Solutions for slow connections (e.g. compression) may affect system capacity elsewhere
- How can I do deep application profiling? (e.g. Blackfire)
- What about single-user load testing? (e.g. running an import with a larger data set than usual)
A Challengr Appears
This will be our system under test
This is what we'll test with*
- Siege - a quick, rather simple command line utility
- k6 - write your tests in JS**, run via a Go binary***
* More tools are listed at the end of this presentation.
** It's JS, but it uses goja, not V8 or Node, and doesn't have a global event loop yet.
*** I've used this on a project significantly more real than Challengr, so that's a big reason we're looking at it today.
#IFNDEF
Load TEst
- <= peak traffic
- Your system shouldn't break
- If it does, it's a stress test
Stress Test
- Trying to break your system
- Surfaces bottlenecks
- Increase traffic above peak or decrease available resources
- Capacity Test is a subset
Soak Test
- Extended test duration
- Watch behavior on ramp down as well as ramp up
- Memory leaks
- Disk space exhaustion (logs!)
- Filled caches
Spike Test
- Stress test with quick ramp-up
- Woot.com at midnight
- TV ad "go online"
- System comes back online
after downtime - Everyone hits your API via
on-the-hour cron jobs
Smoke test
- An initial test to confirm the system operates properly without a large amount of generated load
- May be integration tests in your existing test suite
- May be your load test script, turned down to one (thorough) iteration and one Virtual User (VU)
- Do this before you load test
Now that we've defined our terms...
When?
- When your application performance may change
- Adding/removing features
- Refactoring
- Infrastructure changes
- When your load profile may change
- Initial app launch
- Feature launch
- Marketing pushes/promotions
What are your metrics?
- Speed - response latency
- Scalability - throughput, resource utilization
- Stability - % failed calls/transactions/flows
How should I test?
How should I test?
Accurately.
What should I test?
- Flows, not just single endpoints
- Frequently used
- Performance intensive
- Business critical
Concurrent Requests != Concurrent Users
- Think Time
- API client concurrency
- Caching (client-side or otherwise)
Oversimplification...It's a trap!
- No starting data in database
- No parameterization
- No abandonment at each step in the process
- No input errors
- No think times
- Static think times
- Uniformly distributed think times
- Assuming you have one type of user
- Assuming that a distribution is normal
Vary Your Testing
- High-load Case: heavier endpoints get called more often
- Anticipated Case
- Low-load Case: validation failures + think time
Understand your load test tool
Keep it real
- Use logs/analytics to determine your usage patterns
- Run your APM (e.g. New Relic, Tideways) on your load test env
- Better profiling info
- You'll have the same perf hit as production
- Is your environment code-ified? (e.g. Terraform, CloudFormation)
- Easier to copy envs
- Cheaper to set up an env for an hour to run a load test
- Decide whether testing from near your env is accurate enough
- Test autoscaling/load-shedding facilities
Aggregate your metrics repsonsibly
Average- Median (~50th percentile)
- 90th, 95th, 99th percentile
- Standard Deviation
- Distribution of results
- Explain your outliers
Bottlenecks
- Web Server + Database
- FPM workers/Apache processes
- DB Connections
- CPU + RAM utilization
- Network utilization
- Disk utilization (I/O or space)
- Load balancer
- Network utilization/warmup
- Connection count
- External Services
- Rate limits (natural or artificial)
- Latency
- Network egress
- Queues
- Per-job spin-up latency
- Worker count
- CPU + RAM utilization
- Workers
- Broker
- Queue depth
- Caches
- Thundering herd
- Churning due to
cache evictions
Bottleneck Gotchas
- Just because a request is heavy doesn't mean
it's the biggest source of load - As a system reaches capacity you'll see
nonlinear performance degradation
Let's fix some bottlenecks...
Bonus material: More Tools
-
Tsung
- Erlang (efficient, high volume from a single box)
- Flexible (not just HTTP)
- XML based config
-
The Grinder
- Java-based
- Java, Jython or Clojure scripts
-
Bees With Machine Guns
- Uses EC2 instances
- Python-based
- Goad (Go inside Lambda)
-
Gatling (Java-based)
- Tests in Scala...
- ...or use the recorder
- ab
- httperf
- Apache JMeter
BONUS MATERIAL: Even More Tools!
-
Artillery.io
- Node-based
- Simple stuff in Yaml, can switch to JS (including npm)
-
Molotov (by Mozilla)
- Python 3.5+, uses async IO via coroutines
Thanks! Questions?
- ian.im/loadmw19 - these slides
- joind.in/talk/7e1cd - rate this talk!
- github.com/iansltx/challengr - this code
- twitter.com/iansltx - me
- github.com/iansltx - my code
- Performance Testing Guidance for Web Applications (from Microsoft)
- Blazemeter Blog
Load Testing Your App - MidwestPHP 2019
By Ian Littman
Load Testing Your App - MidwestPHP 2019
Want to find out which pieces of your site break down under load first, so you know how you'll need to scale before your systems catch fire? Load testing answers this question, and these days you can simulate full user behavior in a load test, rather than merely hammering a single endpoint. In this talk, we'll go through a number of conceptual points that you won't want to miss in order for your load tests to perform their intended purpose. Then we'll jump into implementation details, using the K6 load test tool to build a load test that exercises an application in a way that's similar to what we'd see in real life.
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