The Joy of Using Docker

I’ve written about Docker before, as I am a big fan of it. And for this post, I’m going to talk about some practical situations in which I’ve used Docker in real life, both for testing and software development!

Docker Logo

But first, let’s recap what Docker IS and IS NOT:

  • Docker containers spin up quickly (1-2 seconds or less)
  • Docker containers DO have separated process tress and filesystems
  • Docker containers ARE NOT virtual machines
  • Docker containers ARE intended to be ephemeral. (short-lived)
  • You CAN, however, mount filesystems from the host machine into Docker, so those files can live on after the container shuts down (or is killed).
  • You SHOULD only run one service per Docker container.

Everybody got that? Good. Now, let’s get into some real life things I’ve used Docker for.

Experimenting in Linux

Want to test out some commands or maybe a shell script that you’re worried might be destructive? No worries, try it in a Docker container, and if you nuke the filesystem, there will be no long-term consequences.

#
# Start a container with Alpine Linux
#
$ docker run -it alpine

#
# Let's do something dumb
#
$ rm /bin/ls 
$ ls -l
/bin/sh: ls: not found

#
# Just exit the container, restart it, and our filesystem is back!
#
/ # exit 
[unifi:~/tmp ] $ docker run -it alpine
/ # ls
bin    dev    etc    home   lib    media  mnt    proc   root   run    sbin   srv    sys    tmp    usr    var

And all of the above takes just a couple of seconds! This works with other Linux distros as well, such as CentOS and Unbuntu–just change your Docker command accordingly:

docker run -it centos
docker run -it ubuntu

Yes, that means you could run CentOS in a container under Ubuntu or vice-versa. Docker doesn’t care. 🙂

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Fixing Image Sizes on WordPress Attachment Pages

One of the neat things about WordPress is that when you upload an image and then include that image in a blog post, you can decide where that image links to. The image can link to nothing at all, the raw image, or an “attachment page” which contains that image and a caption.

That said, something that has caused me grief for out of the box WordPress builds has been the image on the media page being really small. Take for example, this picture of a freeloading cheetah. When I upload the picture, the attachment page looks like this:

Just look at that. A tiny image and a bunch of the page being completely unused. Disgraceful. Surely we can do better!

As it turns out, tweaking a single line of code can be used to change the size of all images on media pages.

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Scaling Anthrocon’s Website to Handle 1,400 Simultaneous Connections

The Challenge

When hotel reservations open, that is the single busiest time of the year for Anthrocon’s webserver. In fact, it even caused us performance problems last year. That was not so good.

So this year, I decided to try something different. Instead of leaving the regular website up and running, which involves using Drupal, I instead decided to replace the entire page with a relatively static “countdown” page, which displayed a countdown timer and automatically started displaying the hotel link at 11 AM on the opening day.

First, some stats for the Anthrocon website:

  • Peak bandwidth: 1.6 Megabits/sec
  • Peak connections: 1,400 concurrent connections

And now some status for Passkey, who handled most of the traffic:

  • Peak bandwidth: 190 Megabits/sec
  • Peak connections: 4,000 concurrent connections
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