Preparing for the FloodHow to Load Test to Prepare your WordPress site for a viral event.

Who is this idiot? My name is Robert Li.I’m a Solutions Engineer for WP Engine.

I’ve founded 3 startups and exited 1.I have a 3 year old teacup pomeranian named Chelsey.I am a long suffering Knicks fan.I love making WordPress do weird, wonderful things.

Takeaways1. Solutions2. Why Load Test?3. What do you need?4. (Pray to the Demo Gods)5. Demo6. How do you prepare?7. Let’s take a look

Degree of Difficulty: Nerd

The problem

Your Site

You’ve created a site with lots of cool features, that has a great user experience, and that you’ve spend tonne’s of money (or time) on.

Your Hosting

You’ve signed up to some hosting that will fit your new site, in its current state.

It works great!

The Flood

You send a shirt to an influencer, they wear it, you actually start selling stuff, which is great!

Then your site goes down.

WHAT HAPPENED...

So how many cars can I

actually fit?

SolutionLet’s do some load testing!

Why Load Test?

Functional Tests don’t reflect the Real World

Testing the functionality of your site or application doesn’t reflect how users will

use it in real life. They may run across bottlenecks in complex situations your

testing can’t account for.

Your code can behave differently under load

Any changes to code to an established website can cause it to behave

differently under load. Bugs can appear that you didn’t detect in other testing.

Servers perform differently under stress

When scaling to 100s, 1000s or potentially Millions of concurrent users, you may get completely different results for CPU load, error rate, I/O throughput,

and response times.

Houston we have a

problem

The cost of failure is extremely high.50% of users will leave if a page takes longer than 6.5s to load. 1 minute of

downtime during Black Friday costs US$4700 on average. Downtime during a peak traffic event damages brand integrity and creates a snowball effect.

https://royal.pingdom.com/page-load-time-really-affect-bounce-rate/https://www.blazemeter.com/blog/why-load-testing-is-important/

What do you need?

ExecutionHow do you execute a load test?

ReactionHow does the server react to the

load test?

Load Testing Terms Primer

Scenarios - A template or script of what a user might do on a site.

Virtual Users/User Agents - Simulated users

Concurrency - How many actions and users are happening and on the site at any given time

504, 502, 429 errors - When the server is either crapping itself, or protecting itself from “crapping itself”.

.yaml - The file format that holds scenarios

ExecutionIngredients:

Servings: 1000vu

● Taurus - Open source, creates the Virtual Users that perform scenarios.

● Blazemeter - Visualizes the data (can also execute load tests)

● jMeter - Software to help you build and tweak scenarios

● Blazemeter Chrome Extension - Records your actions on a website to start as the basis for a scenario

ReactionIngredients:

Servings: 1 overloaded server

htop sar -q 1

● Stackdriver/Cloudwatch - Server monitoring (GCP/AWS). OpenNMS is agnostic & open source.

● New Relic - Monitoring the application (WordPress) itself.

● Pingdom/Uptime Robot/freshping - Measures whether the website is up.

● htop/sar -q 1 - Command Line (CLI) Live monitoring.

CAVEATS

DO NOT LOAD TEST…

❏ On your production environment

❏ On a shared environment❏ Without telling your host’s

support/security team❏ On a site or web

application you don’t have permission to blast.

x

xx

x

LET’S START

How do you prepare?

Do as much as possible before testing

Decide what to complete and what to defer.

Bottlenecks found in functional testing? Optimize to get a true to life response.

Deciding Test TypeSpike - How does a system respond to a sudden increase and decrease in load? e.g. A Live Online Event

Stress - How does a system respond to consistent high intensity loads? Where does it fail? How does it recover? e.g. A Flash Sale

Soak - How does a system respond to high load over time? e.g. Black Friday

Creating Realistic Scenarios

Start with the user journey

Your marketing and web team are integral to generating realistic test scenarios.

Have them map out ~5 user profiles and journeys. Usually this is their funnel

● From where and how do users access the site?

● What do they do on the site?● How do they arrive? In waves?● How long do they stay?

Determine your KPIsWhat is acceptable? Not what is ideal. What level of existence are

you willing to accept?

Considerations:● Response Time● Error %● Ratio of failed to successful

transactions● Maximum requests per second● Apdex Score

Start small before scaling up big...

Do small scale testing to discover errors and bottlenecks in your own scenarios and with

your own tech stack.

Common Questions to ask yourself:

● Is the script broken?● Is it calling on a resource that

doesn’t exist or performing an impossible action?

● Is the testing platform actually the bottleneck?

● Are there optimizations I can make to improve headroom?

What is the tipping point?When does acceptable become unacceptable?

Under load is 80% usageTest for 120% usage

When number of hits/s plateaus this indicates:

● System can no longer support extra concurrent requests

● You are at max concurrent users.

LET’S TAKE A LOOK

WHAT DO YOU DO NOW?Analyze > Tune > Retest > Rinse and Repeat

https://wpengine.com/blog/preparing-for-the-holiday-rush-a-load-testing-guide/

Questions?Robert LiE: robert.li@wpengine.com P: +61-(0)-7-5613-1084SM: LinkedIn (Look Left!)https://www.linkedin.com/in/robert-liDownload: https://dsh.re/896ac