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One of the selling points of containers is that containerized applications are generally faster to deploy than virtual machines. Containers also usually perform better. But just because containers are faster by default than alternative infrastructure doesn’t mean that there are not ways to make them even faster. You can go beyond the defaults by optimizing Docker container image build time, performance and resource consumption. This post explains how.
Before we delve into Docker optimization tips, let me first explain what I mean when I write about making containers “faster.” Within the context of a conversation about Docker, the word faster can have several meanings. It can refer to the execution speed of a process or an application that runs inside a container. It can refer to image build time. It can refer to the time it takes to deploy an application, or to push code through the entire delivery pipeline. In this post, I’ll consider all of these angles by discussing approaches to making Docker faster in multiple ways.
The following strategies can help make Docker containers faster.
The more code you have inside your image, the longer it will take to build the image, and for users to download the image. In addition, code-heavy containers may run sub-optimally because they consume more resources than required. For all of these reasons, you should strive to keep the code that goes into your container images to the bare minimum that is required for whatever your image is supposed to do. In some cases, designing minimalist container images may require you to rearchitect your application itself. Bloated applications will always suffer from slow deployment and weak performance, whether you deploy them in containers or in something else. You should also resist the temptation, when writing your Dockerfile, to add services or commands that are not strictly necessary. For example, if your application doesn’t need an SSH server, don’t include one. For another example, avoid running apt-get upgrade if you don’t need to.
apt-get upgrade
One of the greatest benefits of containers as compared to virtual machines is that containers don’t require you to duplicate an entire operating system to host an application. To take advantage of this feature to greatest effect, you should host your images with an operating system that does everything you need, and nothing more. Your operating system shouldn’t include extra services or data if they do not advance the mission of your Docker environment. Anything extra is bloat, which will undercut the efficiency of your containers. Fortunately, you don’t have to build your own minimalist operating system for Docker. Plenty of pre-built Linux distributions with small footprints are available for hosting Docker, such as RancherOS.
Image build time is often the biggest kink in your continuous delivery pipeline. When you have to wait a long time for your Docker images to build, you delay your entire delivery process. One way to speed image build time is to use registry mirrors. Mirrors make builds faster by reducing the amount of time required to download components when building an image. Combining multiple RUN commands into a single command also improves build time for images because it reduces the number of layers in your image, which improves build speed, and optimizes the image size to boot. Docker’s build cache feature is another useful way to improve build speed. The cache allows you to take advantage of existing cached images, rather than building each image from scratch. Finally, creating minimalist images, as discussed above, will speed build time, too. The less you have to build, the faster your builds will be.
For staff at many organizations, the greatest obstacle to deploying containers quickly and efficiently results from the complexity of building and managing a containerized environment themselves. This is why using a Containers-as-a-Service platform, or CaaS, can be handy. With a CaaS, you get preconfigured environments, as well as deployment and management tools. A CaaS helps to prevent the bottlenecks that would otherwise slow down a continuous delivery chain.
By default, each container can consume as many resources as it wants. This may not always be ideal because poorly designed or malfunctioning containers can eat up resources, thereby making other containers run slowly. To help prevent this problem, you can set quotas on each container’s compute, memory and disk I/O allotments. Just keep in mind, of course, that misconfigured quotas can cause serious performance problems, too; you therefore need to ensure that your containers are able to access the resources they require.
Even if your containers are already fast, you can probably make them faster. Optimizing what goes into your images, improving image build time, avoiding operating system bloat, taking advantage of CaaS and setting resource quotas are all ways to improve the overall speed and efficiency of your Docker environment.
Chris Tozzi has worked as a journalist and Linux systems administrator. He has particular interests in open source, agile infrastructure and networking. He is Senior Editor of content and a DevOps Analyst at Fixate IO.