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Varnish is a versatile reverse HTTP proxy that caches responses from backend servers in memory so they are served quickly when requested again. It uses HTTP headers to determine whether to cache the responses to a particular request. By default, it does not cache responses with cookies because those are considered client-specific requests; however you can change this setting in the configuration file.
Besides acting as a caching server, Varnish can be used as a:
There are three locations where the HTTP cache can be saved:
Note: For more information about HTTP caching, see this tutorial on HTTP headers and caching strategies.
In this tutorial, you will set up Varnish as a caching reverse proxy server. You’ll then test the setup with Varnish against a non-caching configuration using wrk.
To complete this tutorial, you will need:
To start, you’ll install Apache and Varnish. First update apt-get
, and then install Apache with these commands:
- sudo apt-get update
- sudo apt-get install apache2 -y
You’ll see output indicating that Apache is being installed.
After the Apache installation process is complete, install Varnish with this command:
- sudo apt-get install varnish -y
You’ll see output indicating that Varnish is being installed.
Next, make sure both packages installed correctly. First, use this command to check the status of Apache:
- sudo systemctl status apache2
The output will look similar to this:
Outputroot@ubuntu-s-1vcpu-2gb-fra1-01:~# sudo systemctl status apache2
● apache2.service - The Apache HTTP Server
Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
Active: active (running) since Wed 2021-08-04 18:58:39 UTC; 4min 10s ago
Docs: https://httpd.apache.org/docs/2.4/
Main PID: 2279 (apache2)
Tasks: 55 (limit: 2344)
Memory: 5.0M
CGroup: /system.slice/apache2.service
├─2279 /usr/sbin/apache2 -k start
├─2281 /usr/sbin/apache2 -k start
└─2282 /usr/sbin/apache2 -k start
Aug 04 18:58:39 ubuntu-s-1vcpu-2gb-fra1-01 systemd[1]: Starting The Apache HTTP Server...
Aug 04 18:58:39 ubuntu-s-1vcpu-2gb-fra1-01 apachectl[2278]: AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerName' di>
Aug 04 18:58:39 ubuntu-s-1vcpu-2gb-fra1-01 systemd[1]: Started The Apache HTTP Server.
Press the Q
key to exit the status
command.
Next, check the status of Varnish with this command:
- sudo systemctl status varnish
The output will look similar to this:
Outputroot@ubuntu-s-1vcpu-2gb-fra1-01:~# sudo systemctl status varnish
● varnish.service - Varnish HTTP accelerator
Loaded: loaded (/lib/systemd/system/varnish.service; enabled; vendor preset: enabled)
Active: active (running) since Wed 2021-08-04 18:59:09 UTC; 4min 41s ago
Docs: https://www.varnish-cache.org/docs/6.1/
man:varnishd
Main PID: 3423 (varnishd)
Tasks: 217 (limit: 2344)
Memory: 10.7M
CGroup: /system.slice/varnish.service
├─3423 /usr/sbin/varnishd -j unix,user=vcache -F -a :6081 -T localhost:6082 -f /etc/varnish/default.vcl -S /etc/varnish/secret -s malloc,256m
└─3447 /usr/sbin/varnishd -j unix,user=vcache -F -a :6081 -T localhost:6082 -f /etc/varnish/default.vcl -S /etc/varnish/secret -s malloc,256m
Aug 04 18:59:09 ubuntu-s-1vcpu-2gb-fra1-01 systemd[1]: Started Varnish HTTP accelerator.
Aug 04 18:59:10 ubuntu-s-1vcpu-2gb-fra1-01 varnishd[3423]: Debug: Version: varnish-6.2.1 revision 9f8588e4ab785244e06c3446fe09bf9db5dd8753
Aug 04 18:59:10 ubuntu-s-1vcpu-2gb-fra1-01 varnishd[3423]: Version: varnish-6.2.1 revision 9f8588e4ab785244e06c3446fe09bf9db5dd8753
Aug 04 18:59:10 ubuntu-s-1vcpu-2gb-fra1-01 varnishd[3423]: Debug: Platform: Linux,5.4.0-73-generic,x86_64,-junix,-smalloc,-sdefault,-hcritbit
Aug 04 18:59:10 ubuntu-s-1vcpu-2gb-fra1-01 varnishd[3423]: Platform: Linux,5.4.0-73-generic,x86_64,-junix,-smalloc,-sdefault,-hcritbit
Aug 04 18:59:10 ubuntu-s-1vcpu-2gb-fra1-01 varnishd[3423]: Debug: Child (3447) Started
Aug 04 18:59:10 ubuntu-s-1vcpu-2gb-fra1-01 varnishd[3423]: Child (3447) Started
Aug 04 18:59:10 ubuntu-s-1vcpu-2gb-fra1-01 varnishd[3423]: Info: Child (3447) said Child starts
Aug 04 18:59:10 ubuntu-s-1vcpu-2gb-fra1-01 varnishd[3423]: Child (3447) said Child starts
If you do not see both services up and running, wait a few minutes until they are fully loaded, and keep both of them running.
Now that you have Apache2 Varnish, installed, you’ll give Varnish something to serve, in this case Apache’s static web page.
In the previous step, you installed Varnish, and next you’ll need to configure it. By default, Varnish listens on port 6081 and connects to a local web server on port 8080. You’ll change that to serve the Apache static site from Apache server.
First, you’ll change Varnish’s listening port to 8080. Usually you would want the listening port to be 80, but because you are running Apache and Varnish on the same server, you’ll use port 8080 for Varnish and port 80 for Apache.
There is no configuration option to change the listening port for Varnish, so you’ll do it using the command line. You’ll create a file called customexec.conf
in a new directory called varnish.service.d
in /etc/systemd/system/
that will change the default ports.
Use the mkdir
command to create the new directory:
- sudo mkdir /etc/systemd/system/varnish.service.d
Use your favorite text editor to create a new file called customexec.conf
:
- sudo nano /etc/systemd/system/varnish.service.d/customexec.conf
In customexec.conf
, add the following content:
/etc/systemd/system/varnish.service.d/customexec.conf file[Service]
ExecStart=
ExecStart=/usr/sbin/varnishd -j unix,user=vcache -F -a :8080 -T localhost:6082 -f /etc/varnish/default.vcl -S /etc/varnish/secret -s malloc,256m
In this file you are changing the Service
section of the Varnish configuration. First you remove the old value for the ExecStart
option, and then you assign a new value for it.
The new value specifies the binary file used to run Varnish with the following options:
-j
: Specifies the jailing mechanism to use. Varnish jails are used to reduce the permissions for the varnish process over various platform-specific methods. Here you’re using the unix
mechanism and the user vcache
to limit the permissions. This is default for varnish on Ubuntu systems.
-F
: Indicates that the server should run in the foreground, because systemd
expects the main process to keep running so it can track it, and not fork a new process and die.
-a
: This flag is used to specify the IP address and port for accepting client connections. The IP in this case is empty, which means the server will accept all IPs. The port is set to 8080
.
-T
: This flag specifies the IP address and port for management interface, in this case localhost
and port 6082
.
-f
: This flag specifies the default VCL file for Varnish configuration. You will edit this file later in this tutorial to configure Varnish to connect to the Apache server.
-S
: This flag specifies a shared secret file for authorizing access to the management interface. The /etc/varnish/secret
value is the default for Varnish on Ubuntu. You will not use the secret file in this tutorial.
-s
: This flag indicates where and how to store objects. The value malloc,256m
is the default one for Vanish. It means to store various Varnish objects in memory using the malloc
system call and a maximum size of 256 megabytes. Other possible values are default
, which uses umem
when malloc
is not available, or file
, which stores objects in a file on the disk.
Save and close the customexec.conf
file. Then execute this command to reload the systemd
services file from disk:
- sudo systemctl daemon-reload
Then restart Varnish for changes to take effect.
- sudo systemctl restart varnish
You won’t see any output from these last two commands. To make sure that Varnish is now listening on port 8080, use the netstat
command to display all listening TCP sockets on the server.
- sudo netstat -ltnp | grep 8080
You’ll see output that looks like this:
Outputtcp 0 0 0.0.0.0:8080 0.0.0.0:* LISTEN 18689/varnishd
tcp6 0 0 :::8080 :::* LISTEN 18689/varnishd
Now that Varnish is running and listening to port 8080, you need to edit the default configuration file located at /etc/varnish/default.vcl
:
- sudo nano /etc/varnish/default.vcl
Navigate to the backend default
block, and then change .port
to 80
, as shown here:
default.vcl file
# Default backend definition. Set this to point to your content server.
backend default {
.host = "127.0.0.1";
.port = "80";
}
Save and close the default.vcl
file, then restart Varnish with this command:
- sudo systemctl restart varnish
If everything is fine, there won’t be any output. Open http://your_server_ip:8080
in your browser, and you’ll see the Apache static site, opened using Varnish.
You now have Apache and Varnish running together on the same Droplet, with Apache listening to port 80 and Varnish to port 8080. Next, you’ll compare the response times of both servers using the wrk tool.
wrk is a modern HTTP benchmarking tool. It is written in C, and can be used to load test web servers with many requests per second. In this step, you’ll use wrk to run tests against Apache and Varnish and then compare the results.
First you’ll need to install wrk by building it from source. Start by installing some build tools for C and git, which are required for building wrk from source:
- sudo apt-get install build-essential libssl-dev git unzip -y
Then clone the git repository for wrk into the wrk
directory:
- git clone https://github.com/wg/wrk.git wrk
Change to that new directory:
- cd wrk
Build the wrk executable with the make
command:
- make
Copy wrk to the /usr/local/bin
directory so you can access it from anywhere in your directory structure:
- sudo cp wrk /usr/local/bin
Now that you have wrk installed, use it to test the responsiveness of Apache with this command:
- wrk -t2 -c1000 -d30s --latency http://server_ip/
This command uses the following arguments:
-t2
: This means run two threads.-c1000
: Keep 1000 HTTP connections open.-d30s
: Run the test for 30 seconds.--latency
: Print latency statistics.Wait 30 seconds until the test is done, and you’ll see output similar to this:
outputRunning 30s test @ http://68.183.115.151/
2 threads and 1000 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 44.45ms 104.50ms 1.74s 91.20%
Req/Sec 8.29k 1.07k 12.40k 71.00%
Latency Distribution
50% 11.59ms
75% 22.73ms
90% 116.16ms
99% 494.90ms
494677 requests in 30.04s, 5.15GB read
Socket errors: connect 0, read 8369, write 0, timeout 69
Requests/sec: 16465.85
Transfer/sec: 175.45MB
In this test, the average latency is 44.45ms, there were 494,677 total requests, 8,369 read errors, and 69 timeout errors. The exact numbers will vary in your installation.
Now run the same test again for the Varnish server using this command:
- wrk -t2 -c1000 -d30s --latency http://server_ip:8080/
Wait 30 seconds until the test is done, and you’ll see output similar to this:
outputRunning 30s test @ http://68.183.115.151:8080/
2 threads and 1000 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 14.41ms 13.70ms 602.49ms 90.05%
Req/Sec 6.67k 401.10 8.74k 83.33%
Latency Distribution
50% 13.03ms
75% 17.69ms
90% 24.72ms
99% 58.22ms
398346 requests in 30.06s, 4.18GB read
Socket errors: connect 0, read 19, write 0, timeout 0
Requests/sec: 13253.60
Transfer/sec: 142.48MB
The output you see will likely be somewhat different, but the latency will be lower for Varnish than for Apache. In this case, the average latency is 14.41ms, there were 398,346 total requests, and no errors.
In these tests, with Apache the average response time was 44.45ms with 8,438 errors, while Varnish achieved an increase in speed to 14.41ms, and also had no errors. This is because Varnish cached the response in memory and served it for later requests, unlike Apache, which needs to read from disk almost every time the resource is requested.
In this tutorial, you configured Varnish as a reverse proxy caching server for a static web site. You saw how to use basic HTTP caching to improve performance, and you used wrk to run load tests for the Apache and Varnish servers to compare the results.
You’ve seen that the Varnish cache server speeds up your static site by serving content from main memory and not requesting it from the back end Apache server every time a new request arrives. For more information about other uses of Varnish, see the official documentation.
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I need to create a reverse proxy to cache our backend responses for 1 second (so the data will stay fresh but there will be a single query run against the database per second)
What is your opinion for Varnish vs NGINX as reverse proxy?
Thanks