March was a great month for Kernl! We did some blogging, a bunch of infrastructure work, and a little bit of unplanned work due to API deprecation at BitBucket.
Features & Updates
Resource Starvation (Load Testing) – We’ve decreased the number of users per machine that Kernl WordPress Load Testing uses. This helps prevent resource starvation on the load generation servers.
Pre-Configured Load Tests – Kernl now has 4 different pre-configured load tests to make testing your site’s performance even easier!
BitBucket API Update – BitBucket API calls now use Oauth2 and their v2 endpoints. The v1 endpoints are going away in April.
Analytics – All of the features available in Kernl Analytics Agency plan have been rolled into one single plan at the same $10/month price point as the small plan. We also increased data retention to 365 days to make our comparison tool more useful.
Load Test Working Indicator – Load tests will now show a “working” indicator when in a state before the load test has started but after you have submitted your request to start a load test.
MongoDb Driver – The MongoDB driver that we use has been upgraded for better connection retry handling.
Updates – Kernl Analytics and Kernl WordPress Load Testing have been upgraded to Node.js 10.15.3 and have had all of their packages updated.
License Management Widget – The license management widget was throwing an error when no error was present. This has been resolved.
In the world of WordPress performance, you can’t go far without talking about caching plugins. I’ve personally used several different caching plugins throughout my time as a WordPress developer but have never really took the time to see how the plugins perform under pressure. Until now.
Over the next couple of months I’ll be releasing a series of blog posts detailing the performance characteristics of different WordPress caching plugins. This DOES NOT include server caching plugins (LiteSpeed, Varnish, Nginx Fast CGI, etc) because those are in a league of their own and it wouldn’t really be an “apples to apples” comparison.
I decided to try and run this comparison as if I were looking for a cheap VPS provider and hoping to get a lot of performance out of it. Since I’m a huge Digital Ocean fanboy, I went ahead and used the pre-built WordPress image in their marketplace and dropped it on a $5/month droplet. This leaves me with a typical LAMP setup with mostly default configurations for everything. I also wanted to test the configuration with Memcachedso that was installed as well.
In order to fully test W3 Total Cache I ran the following tests with 200 concurrent users out of Digital Ocean’s NYC3 data center. The server under test was located in Amsterdam.
Baseline Test – No caching at all. We just need to see what performance we can get without caching enabled.
Fragment Cache Only (Memcached)
Database Cache Only (Memcached)
Page Cache Only (Memcached)
All Caches Enabled (Memcached)
All Caches Enabled (OPCode APC)
All Caches Enabled (Disk Enhanced[page] & Disk)
It is important to note that W3 Total Cache will also do HTML, CSS, and JS minification. I’m not particularly interested in that, but do know that it can compress these outputs with a variety of different tools and may decrease overall load time.
High Level Results
W3 Total Cache is a solid caching plugin that gives you a lot of different options for getting good performance out of WordPress.
Response Time (90%)
Fragment Cache Only
Database Cache Only
Page Cache Only
All Caches (Memcached)
All Caches (OPCode APC)
All Caches (Disk)
As expected the baseline load test didn’t perform the greatest. It is no secret that WordPress doesn’t perform well under load without caching plugins, but we needed a baseline anyways.
We peaked at around 19 req/s and then started to trail off towards 5 req/s as the error rate increased. Looking at the response time distribution, you can see that things didn’t look much better.
I mean it could be worse. At least people could access your site in under 5 seconds, but most people bail in 1 second or less.
Fragment Cache Only
The fragment cache in W3 Total Cache is supposed to “reduce time for common operations”. I’m not sure what that means but by itself it didn’t seem to help me out very much.
With fragment caching enabled we still see a similar request and failure profile as when we didn’t have any caching enabled at all.
Response time distribution was similar to no caching. My guess is that fragment caching optimizes a very narrow set of operations and that my blog doesn’t really use any of them.
Database Cache Only
I expected to see some pretty good performance with the database cache enabled. Presumably this cached queries to MySQL with should have really helped us scale. It didn’t 🙁
You can see that we were just slightly better than with the fragment cache, but not even close to where I thought we would be.
The response time distribution was bad too. It actually is a bit higher than the other ones. I assume that this was just a fluke and that if I ran this test several times it would be the same as the others.
Page Cache Only
With full page caching enabled we start to see some good performance improvements.
The graph above shows that we hit about 60 req/s before the wheels start to fall off, but even then we’re able to continue serving requests at a respectable 50-ish req/s.
The response time distribution looks a lot better here as well. 90% of requests finished in 1.1 seconds. This isn’t bad at all considering you’re going at > 50 req/s.
All Caches Enabled (Memcached)
With all caches enabled we start to see some pretty impressive performance out of W3 Total Cache.
130 req/s is solid, but you’ll notice there is a steady stream of errors coming across as well. In general I would say that this setting is good to prevent to your site from going down but that you should look to increasing resources ASAP.
Response time distribution is where we start to see some really excellent gains. The pages were served almost immediately with the 99th percentile being 220ms. Much of that time can be attributed to latency due because the servers are so far apart.
All Caches Enabled (OPCode APC)
I expected the results of this test to be similar to Memcached because they’re both in-memory caches, but that wasn’t even close to true.
We initially peaked at 60 req/s and then started to see a large uptick in errors. Requests eventually started to climb back up, but the error rate stayed consistent.
I was pretty disappointed in the response time distribution. I expected it to be similar to Memcached but it looks like OPCode APC just isn’t as efficient. 90th percentile at 1.8s isn’t terrible but it isn’t good either.
All Caches Enabled (Disk)
Disk-based caching is very likely the type you would be using if you were in a shared hosting environment. The good news is that the disk-based caching that W3 Total Cache does is quite good.
133 req/s with a fairly small error rate is great! At this level you could easily handle 99% of the traffic scenarios you’ll see as a WordPress developer.
The response time distribution was similar to the Memcached version of this test in that 99% of requests finished in under 170ms. Not bad considering WordPress was fielding > 130 requests per second.
W3 Total Cache is an excellent choice for caching. While some of its configuration can be confusing, you can still get very acceptable performance by enabling page caching or all caching thats available. Its also worth noting that you could very likely get excellent performance with no errors if you tweaked some Apache and MySQL settings in addition to using W3 Total Cache.
Throughout the lifetime of Kernl I’ve always kept an eye out for ways to reduce costs, which means I’ve constantly got an eye on Digital Ocean‘s droplet pricing to see if there are any cost efficiencies to be had. Back in January of 2018 Digital Ocean released what they called “flexible” plans. These plans are 3 droplet types that all cost $15/month, but have 3 different configurations:
3GB RAM, 1 vCPU
2GB RAM, 2 vCPUs
1GB RAM, 3 vCPUs
I recently re-discovered these plans and thought to myself “Jack, you should load test these configurations and see which is better for WordPress!”. So here we are, attempting to answer the age-old question “Is RAM or CPU more important for WordPress performance?”.
As with the $5 VPS shootout, I used the setup guide posted here to get a consistent setup across the different servers. I ended up with the following software versions:
PHP FPM 7.2
Ubuntu 18.04 LTS
The WordPress server location was in Digital Ocean’s London (lon1) data center and the load generators were located in Digital Ocean’s New York City 3 (nyc3) data center.
No caching was used for this test because I wanted to test WordPress performance, not caching plugin performance.
The test WordPress site was populated with a WP export dump of this blog. That means that the test skewed extremely read-heavy. Your results may be different for a site that is write-heavy, but experience tells me that this probably isn’t true given how chatty WordPress is with MySQL in most situations.
Test A: 3GB RAM, 1 vCPU
The first test that I ran against the $15 droplet was with the 3GB RAM and 1 vCPU configuration. I had expected this to perform the worst out of any of the configurations due to WordPress generally being CPU bound when it comes to performance.
As you can see things went OK until we hit around 18 requests per second, and then everything went off the rails. This isn’t too surprising as I didn’t have any caching plugins installed. This is just raw WordPress with MySQL (MariaDB). I ended up killing the load test after 7 minutes because it was clear what the results were.
The response time distribution was also pretty terrible with a 99th percentile of slightly over 5 seconds.
Test B: 2GB RAM, 2 vCPUs
Next up was the 2GB of RAM with 2 vCPUs $15 configuration. I had actually thought that this configuration would perform the best due to the nice balance of RAM and CPUs. It performed better than the first test, but it wasn’t the best.
As you can see we had far fewer errors this time and were able to reach 60 requests per second. For those doing the math that is 3.3x better performance than a single vCPU (for the same price!).
The response time distribution was starting to look better with 2 vCPUs as well. The 99th percentile was ~2.7 seconds which isn’t too bad while serving 60 requests per second (5.1 million requests per day).
Test C: 1GB RAM, 3 vCPUs
Finally I tested the 1GB RAM, 3 vCPUs $15 configuration. Personally I thought that this would perform 2nd best because I figured the server would become RAM starved while trying to server more requests. I was wrong.
So for the same price as the 3GB RAM, 1 vCPU server we can get 6.5x the performance by simply choosing the configuration with more CPU availability. We peaked at around 118 requests per second (10.1 million requests per day) and then it started to trail off as we started to see errors.
The response time distribution was pretty excellent here and started to look like what we would see from high performance servers (1 big outlier with generally good response times across the rest of the spectrum). With the 99th percentile at 700ms it seems like a no-brainer to go with more vCPUs.
It seems obvious from the data presented above that you are always better off going with more vCPUs than RAM, but I hesitate to always recommend that because reality is more complicated. There are likely situations where a good balance of RAM and vCPUs would perform better (lots of image uploads and processing for example).
So what does this all mean? In most cases you are probably better off with more vCPUs instead of more RAM. However, I strongly recommend that you do some load testing to make sure that this is true for your WordPress site.
In the world of affordable WordPress hosting there is an array of different VPS providers to choose from. With so many choices how do you know who to choose? In addition to criteria such as ease of use and support, performance is a huge concern for most people deploying WordPress. In this article we’ll take a look at the performance of several different VPS providers in the $5 tier to see how they perform under load by using Kern’s WordPress Load Testing feature.
Who are we testing?
There are a lot of VPS providers out there providing machines in the $5 / month tier, so we’ve chosen 7 of the more popular providers to test against:
No Cache – 200 concurrent users for 30 minutes. We used this test to see raw WordPress performance with no caching enabled.
Cached with W3 Total Cache + Memcached – 200 concurrent users for 30 minutes. We used this test to see what a more real-world scenario looks like. In general most people use some form of caching on their site.
To make sure that our test setup was consistent across all VPS providers we followed this setup guide, where we ended up with the following versions of software:
With regards to regions, for every test we kept the VPS instances on the east coast of the United States with the exception of Hetzer where we had the VPS instance in Germany.
Results (Request & Failures)
First, let’s take a look at the request / second results across the different providers.
As you can see there is a wide spread of results depending on host. Honestly this wasn’t want I expected when I started. You’ll also notice that the Azure box cost $15/month. It was the closest I could get to finding a $5/month box in their interface (which I felt like I needed another degree in Computer Science to understand!).
So let’s visualize the data with no caching enabled.
We get lots of interesting results here. If you run a site where caching is difficult to do, your $5 will go much further depending on your host. Some notes:
Google Cloud and Azure performed TERRIBLE. I’m not sure why. Maybe it had to do with accessing the disk so frequently to load up PHP files? (but I expect that those were cached by PHP FPM or some other underlying process).
If you are in Europe, Hetzner is your friend. $5/month gets you 4x the ram and 2x the vCPUs are the next closest provider.
If you are in the US, AWS seems to be winning in this test but not by much. It feels like you would be fine going with Digital Ocean or Vultr.
Before making any real decisions on a host, I’d want to run 5 or so tests across different instances to make sure that there isn’t a lot of variance in my results. Noisy neighbors can often be a problem on VPS providers.
Now let’s take a look at a more realistic scenario where you have a caching plugin installed.
You’ll notice that there aren’t any error bars on this graph. Thats because each host was able to handle the load without having any. This isn’t too surprising since most of the requests would be served right out of memory via Memcached. Some notes on cached requests:
Once again, Google Cloud and Azure perform the worst out of any of these hosts. Given how highly regarded they are in the hosting ecosystem outside of WordPress I expected better performance.
All of the other providers posted impressive numbers (170 req/s – 180 req/s). At level I would probably choose whatever provider had the best support, user interface, and reliability.
I suspect that most of these boxes could handle a little bit more load before going under. If I increased this test by an order of magnitude (200 users to 2000 users) I think most of the providers would tap out before Hetzner does due to how much more RAM and CPU it has.
Results (Response Time Distribution)
While requests per second and failures per second are valuable metrics, in order to get a more holistic view of raw performance for these $5 VPS instances we need to look at response time distribution.
So how should you interpret this chart? For the percentage columns, each value is in milliseconds. If you look at the 99% column, you can see that 99% of Vultr requests returned in <= 3600ms. If you look at the 80% column for Vultr, you can see that 80% of Vultr requests returned in <= 3400ms. Let’s take a look at our un-cached results.
Some notes on this graph:
Any service that hit the 5000ms mark killed the request. I think that they likely would have gone far beyond that.
Once again, for $5 Hetzner is just crushing it. You simple can’t compete with 4GB RAM and 2vCPUs. Even with no caching their 99th percentile was under 2 seconds!
For our non-european readers, Digital Ocean, Vultr, and AWS seemed to perform the best. AWS remained remarkably consistent across the response time distribution range. This is a good thing.
Google Cloud… wtf? So 99% of your requests finished in <= 5 seconds, and then 90% of requests finished in <= 300ms? Something is fishy.
And now, let’s see how things change when caching is used.
As expected, most providers do very well when caching is used. Digital Ocean, Linode, Vultr, AWS, and Hetzner are all performing in the <= 200ms range (some lower!). It’s hard to decide who is better at this level due to latency due to geographic distance. The point is that you could choose any of those hosts and be OK when using a cache plugin. Once again, I’m struggling to figure out why someone would spend their $5 on Azure or Google Cloud.
Results (Total Requests)
Our final metric we need to look at before we can pass any judgement on our VPS providers is total requests. This in particular needs to be compared with response time distribution.
This graph does a great job explaining some of the discrepancies in the response time distribution data. When caching wasn’t enabled, Google Cloud and Azure barely even show up on the graph. More thoughts:
I’m 90% positive that the Google Cloud and Azure instances nearly stopped processing requests at some point. They were so overwhelmed that they just fell over. The data seems to support this.
Google Cloud and Azure are not the best place to spend $5. Even with caching I would be scared if there was ever a cache-miss.
Hetzner is the clear winner in un-cached data. Once again, this makes sense how much more machine you are getting for your money.
On the U.S. side of the ocean, AWS seems to win here, although not by much over Digital Ocean and Vultr. Once caching is taken into consideration they all perform roughly the same (accounting for latency between data centers and load generators).
If performance is all you care about for your $5 (and thats a big if), then choose Hetzner if you need a VPS in Europe. If you need a VPS in the US or elsewhere, choose AWS, Digital Ocean, or Vultr. Microsoft and Google are not great for $5.