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  100  s 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

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Here s some more benchmarks for Docker based memcached server versus host native memcached server using Twemperf benchmark tool https   github com twitter twemperf with 5000 connections and 20k connection rate  Connect time overhead for docker based memcached seems to agree with above whitepaper at roughly twice native speed   Twemperf Docker Memcached  Connection rate  9817 9 conn s Connection time  ms   avg 341 1 min 73 7 max 396 2 stddev 52 11 Connect time  ms   avg 55 0 min 1 1 max 103 1 stddev 28 14 Request rate  83942 7 req s  0 0 ms req  Request size  B   avg 129 0 min 129 0 max 129 0 stddev 0 00 Response rate  83942 7 rsp s  0 0 ms rsp  Response size  B   avg 8 0 min 8 0 max 8 0 stddev 0 00 Response time  ms   avg 28 6 min 1 2 max 65 0 stddev 0 01 Response time  ms   p25 24 0 p50 27 0 p75 29 0 Response time  ms   p95 58 0 p99 62 0 p999 65 0   Twemperf Centmin Mod Memcached  Connection rate  11419 3 conn s Connection time  ms   avg 200 5 min 0 6 max 263 2 stddev 73 85 Connect time  ms   avg 26 2 min 0 0 max 53 5 stddev 14 59 Request rate  114192 6 req s  0 0 ms req  Request size  B   avg 129 0 min 129 0 max 129 0 stddev 0 00 Response rate  114192 6 rsp s  0 0 ms rsp  Response size  B   avg 8 0 min 8 0 max 8 0 stddev 0 00 Response time  ms   avg 17 4 min 0 0 max 28 8 stddev 0 01 Response time  ms   p25 12 0 p50 20 0 p75 23 0 Response time  ms   p95 28 0 p99 28 0 p999 29 0   Here s bencmarks using memtier benchmark tool  memtier benchmark docker Memcached  4         Threads 50        Connections per thread 10000     Requests per thread Type        Ops sec     Hits sec   Misses sec      Latency       KB sec ------------------------------------------------------------------------ Sets       16821 99          ---          ---      1 12600      2271 79 Gets      168035 07    159636 00      8399 07      1 12000     23884 00 Totals    184857 06    159636 00      8399 07      1 12100     26155 79   memtier benchmark Centmin Mod Memcached  4         Threads 50        Connections per thread 10000     Requests per thread Type        Ops sec     Hits sec   Misses sec      Latency       KB sec ------------------------------------------------------------------------ Sets       28468 13          ---          ---      0 62300      3844 59 Gets      284368 51    266547 14     17821 36      0 62200     39964 31 Totals    312836 64    266547 14     17821 36      0 62200     43808 90

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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       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      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     Now looking at CPU overhead      Now some examples of memory  read the paper for details  memory can be extra tricky

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Docker isn t virtualization  as such -- instead  it s an abstraction on top of the kernel s support for different process namespaces  device namespaces  etc   one namespace isn t inherently more expensive or inefficient than another  so what actually makes Docker have a performance impact is a matter of what s actually in those namespaces     Docker s choices in terms of how it configures namespaces for its containers have costs  but those costs are all directly associated with benefits -- you can give them up  but in doing so you also give up the associated benefit    Layered filesystems are expensive -- exactly what the costs are vary with each one  and Docker supports multiple backends   and with your usage patterns  merging multiple large directories  or merging a very deep set of filesystems will be particularly expensive   but they re not free  On the other hand  a great deal of Docker s functionality -- being able to build guests off other guests in a copy-on-write manner  and getting the storage advantages implicit in same -- ride on paying this cost  DNAT gets expensive at scale -- but gives you the benefit of being able to configure your guest s networking independently of your host s and have a convenient interface for forwarding only the ports you want between them  You can replace this with a bridge to a physical interface  but again  lose the benefit  Being able to run each software stack with its dependencies installed in the most convenient manner -- independent of the host s distro  libc  and other library versions -- is a great benefit  but needing to load shared libraries more than once  when their versions differ  has the cost you d expect    And so forth  How much these costs actually impact you in your environment -- with your network access patterns  your memory constraints  etc -- is an item for which it s difficult to provide a generic answer

[performance] What is the runtime performance cost of a Docker container?

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