This post will walk you through the steps to running a runc container using the OCI configuration.
We will walk through two examples. One for running a Fedora container and another for running a Redis container.
There are three steps to running a runc container:
- Construct a rootfs
- Create a OCI configuration
- Start the runtime
Getting ocitools
OCItools are a bunch of utilities to work with the OCI specification. We are going to make use of the generate utility. It helps generate a OCI configuration for runc with a command line that is similar to docker run.
$ export GOPATH=/some/dir
$ go get github.com/opencontainers/ocitools
$ cd $GOPATH/src/github.com/opencontainers/ocitools
$ make && make install
Note: OCItools will soon be available as a package on Fedora, RHEL, and CentOS.
Fedora Container
There are various ways to construct a rootfs. Ultimately, it is just a directory with a bunch of files that will be visible and used inside your container. In this example, we will use dnf to construct a rootfs.
First we create a directory for our container:
$ mkdir /runc/containers/Fedora/rootfs
$ cd /runc/containers/Fedora
$ dnf install --installroot /runc/containers/Fedora/rootfs bash coreutils procps-ng iptools
Next we generate a configuration using OCItools:
$ ocitools generate --args bash
This create a config.json in the current directory. By passing --args we change the command to be run to bash from the default.
And finally, we start the container:
$ runc start Fedora
bash-4.3# ps -ef
UID PID PPID C STIME TTY TIME CMD
root 1 0 0 18:02 ? 00:00:00 bash
root 7 1 0 18:03 ? 00:00:00 ps -ef
bash-4.3# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
bash-4.3# ls -l
total 48
lrwxrwxrwx. 1 root root 7 Feb 3 22:10 bin -> usr/bin
dr-xr-xr-x. 2 root root 4096 Feb 3 22:10 boot
drwxr-xr-x. 5 root root 360 Apr 8 18:02 dev
drwxr-xr-x. 29 root root 4096 Apr 8 17:45 etc
drwxr-xr-x. 2 root root 4096 Feb 3 22:10 home
lrwxrwxrwx. 1 root root 7 Feb 3 22:10 lib -> usr/lib
lrwxrwxrwx. 1 root root 9 Feb 3 22:10 lib64 -> usr/lib64
drwxr-xr-x. 2 root root 4096 Feb 3 22:10 media
drwxr-xr-x. 2 root root 4096 Feb 3 22:10 mnt
drwxr-xr-x. 2 root root 4096 Feb 3 22:10 opt
dr-xr-xr-x. 287 root root 0 Apr 8 18:02 proc
dr-xr-x---. 2 root root 4096 Apr 8 17:43 root
drwxr-xr-x. 5 root root 4096 Apr 8 17:45 run
lrwxrwxrwx. 1 root root 8 Feb 3 22:10 sbin -> usr/sbin
drwxr-xr-x. 2 root root 4096 Feb 3 22:10 srv
dr-xr-xr-x. 13 root root 0 Apr 7 22:19 sys
drwxrwxrwt. 2 root root 4096 Apr 8 17:45 tmp
drwxr-xr-x. 12 root root 4096 Apr 8 17:42 usr
drwxr-xr-x. 19 root root 4096 Apr 8 17:45 var
bash-4.3#
We can list the running containers by using runc list in another terminal:
$ runc list
ID PID STATUS BUNDLE CREATED
Fedora 7770 running /runc 2016-04-08T18:02:12.186900248Z
We can exec another process in the container using runc exec:
[root@dhcp-16-129 ~]# runc exec Fedora sh
sh-4.3# ps -ef
UID PID PPID C STIME TTY TIME CMD
root 1 0 0 18:02 ? 00:00:00 bash
root 10 0 0 18:04 ? 00:00:00 sh
root 16 10 0 18:04 ? 00:00:00 ps -ef
sh-4.3# exit
exit
Redis Container
We’ll create a rootfs using dnf just like we did for Fedora:
$ mkdir /runc/containers/redis/rootfs
$ cd /runc/containers/redis
$ dnf install --installroot /runc/containers/redis/rootfs redis
Next, we generate a configuration using OCItools:
$ ocitools generate --args /usr/bin/redis-server --network host
We customize the args to start the redis-server and set network to host, meaning that we will use the host network stack instead of creating a new network namespace for the container.
Next, we start the Redis container:
$ runc start redis
1:C 08 Apr 18:08:22.665 # Warning: no config file specified, using the default config. In order to specify a config file use /usr/bin/redis-server /path/to/redis.conf
1:M 08 Apr 18:08:22.669 # Server started, Redis version 3.0.6
1:M 08 Apr 18:08:22.670 * DB loaded from disk: 0.001 seconds
1:M 08 Apr 18:08:22.670 * The server is now ready to accept connections on port 6379
We have our redis-server up and running!
We can try to connect to it from a redis-cli by exec'ing into the container:
$ runc exec redis redis-cli
127.0.0.1:6379>
127.0.0.1:6379> set name mrunal
OK
127.0.0.1:6379> get name
"mrunal"
127.0.0.1:6379> quit
These are some simple examples to get started with OCI. OCItools generate allows configuring the config with flags. We use the host networking stack as a convenience. In a future post, we will delve into OCI hooks that allow setting up container networking.