CODEWITHSUNDEEP
docker
Dax Fohl
Dax Fohl

Reputation: 10781

Is there a way to speed up docker exec?

Is there a way to eliminate the overhead of docker exec? For example, when I call docker exec ls on an already-running container, it takes 0.15s to return the result.

root@min:/# time docker exec 6f ls
bin
boot
dev
etc
home
lib
lib64
lost+found
media
mnt
opt
proc
root
run
sbin
srv
sys
tmp
usr
var

real    0m0.159s
user    0m0.028s
sys 0m0.028s

However if I start the container attached, and ls from the container's command line, it only takes a couple ms.

root@min:/# docker start -ai 6f
[root@6f384443d3a6 /]# time ls
bin  boot  dev  etc  home  lib  lib64  lost+found  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

real    0m0.004s
user    0m0.003s
sys 0m0.000s

The containers were created as follows:

$ docker create -t -i fedora bash
6f8af538ec541dd581ebc2a24153a28329acb5268abe5ef868c1f1a261221752
$ docker start 6f

What is the overhead in docker exec, and is there a way to reduce it? (I'm trying to make a service that hosts running containers and calls executables on them and returns the results. But if it's going to take 150ms per call, then that's no good).

Upvotes: 2

Views: 1879

Answers (1)

David Maze
David Maze

Reputation: 160000

Docker is implemented as an HTTP-based service, which is usually called over a Unix socket. For example, you can see the "create an exec instance" request in the Docker API documentation. It takes at least two round-trips to run a docker exec command, plus the overhead of starting the host-side docker process. On native Linux the HTTP calls will be over a Unix socket; on other platforms, depending on your setup, it may need to cross a VM boundary or even go over TCP.

150 ms for a single docker exec call intuitively feels a little slow to me, but not out of the realm of the reasonable. There's not much you can do to speed it up, since all of these mechanics are inside the docker client tool and server daemon.

A typical Docker setup will have containers running long-running server processes (not a bare fedora container, and not a bash shell as the main container process). You should be able to make a network request to the container, and this will likely be faster than docker exec (and not require administrator privileges).

Upvotes: 5

Related Questions