Executing remote commands in an OKD container

You can use the CLI to execute remote commands in an OKD container.

Executing remote commands in containers

Support for remote container command execution is built into the CLI.

Procedure

To run a command in a container:

  1. $ oc exec <pod> [-c <container>] <command> [<arg_1> ... <arg_n>]

For example:

  1. $ oc exec mypod date

Example output

  1. Thu Apr  9 02:21:53 UTC 2015

For security purposes, the oc exec command does not work when accessing privileged containers except when the command is executed by a cluster-admin user.

Protocol for initiating a remote command from a client

Clients initiate the execution of a remote command in a container by issuing a request to the Kubernetes API server:

  1. /proxy/nodes/<node_name>/exec/<namespace>/<pod>/<container>?command=<command>

In the above URL:

  • <node_name> is the FQDN of the node.

  • <namespace> is the project of the target pod.

  • <pod> is the name of the target pod.

  • <container> is the name of the target container.

  • <command> is the desired command to be executed.

For example:

  1. /proxy/nodes/node123.openshift.com/exec/myns/mypod/mycontainer?command=date

Additionally, the client can add parameters to the request to indicate if:

  • the client should send input to the remote container’s command (stdin).

  • the client’s terminal is a TTY.

  • the remote container’s command should send output from stdout to the client.

  • the remote container’s command should send output from stderr to the client.

After sending an exec request to the API server, the client upgrades the connection to one that supports multiplexed streams; the current implementation uses SPDY.

The client creates one stream each for stdin, stdout, and stderr. To distinguish among the streams, the client sets the streamType header on the stream to one of stdin, stdout, or stderr.

The client closes all streams, the upgraded connection, and the underlying connection when it is finished with the remote command execution request.