What is the runtime performance cost of a Docker container?

Question

I'd like to comprehensively understand the run-time performance cost of a Docker container. I've found references to networking anecdotally being ~100µs slower.

I've also found references to the run-time cost being "negligible" and "close to zero" but I'd like to know more precisely what those costs are. Ideally I'd like to know what Docker is abstracting with a performance cost and things that are abstracted without a performance cost. Networking, CPU, memory, etc.

Furthermore, if there are abstraction costs, are there ways to get around the abstraction cost. For example, perhaps I can mount a disk directly vs. virtually in Docker.

possible duplicate of Is there a formula for calculating the overhead of a Docker container? — Golo Roden
@GoloRoden that question is similar but not exactly the same. I'm looking for latency costs with reasons like "networking is being passed through an extra layer" whereas that question's accepted answer is more about measuring the costs of the container + app. — Luke Hoersten
I'm glad you posted it though. That question didn't come up in my search. The measurement/metrics article is super useful: blog.docker.io/2013/10/gathering-lxc-docker-containers-metrics — Luke Hoersten
This is a good session titled "Linux Containers - NextGen Virtualization for Cloud" telling performance metrics by comparing docker, KVM VM and bare metal: youtube.com/watch?v=a4oOAVhNLjU — shawnzhu

Hamy Hamy · Accepted Answer · 2014-10-01T20:26:14

An excellent 2014 IBM research paper “An Updated Performance Comparison of Virtual Machines and Linux Containers” by Felter et al. provides a comparison between bare metal, KVM, and Docker containers. The general result is: Docker is nearly identical to native performance and faster than KVM in every category.

The exception to this is Docker’s NAT — if you use port mapping (e.g., docker run -p 8080:8080), then you can expect a minor hit in latency, as shown below. However, you can now use the host network stack (e.g., docker run --net=host) when launching a Docker container, which will perform identically to the Native column (as shown in the Redis latency results lower down).

Docker NAT overhead

They also ran latency tests on a few specific services, such as Redis. You can see that above 20 client threads, highest latency overhead goes Docker NAT, then KVM, then a rough tie between Docker host/native.

Docker Redis Latency Overhead

Just because it’s a really useful paper, here are some other figures. Please download it for full access.

Taking a look at Disk I/O:

Docker vs. KVM vs. Native I/O Performance

Now looking at CPU overhead:

Docker CPU Overhead

Now some examples of memory (read the paper for details, memory can be extra tricky):

Docker Memory Comparison

What is the runtime performance cost of a Docker container?

3 Answers