Peter Kolloch created MESOS-2859:
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Summary: Semantics of CommandInfo shell/value/arguments are very
confusing
Key: MESOS-2859
URL: https://issues.apache.org/jira/browse/MESOS-2859
Project: Mesos
Issue Type: Documentation
Reporter: Peter Kolloch
CommandInfo includes the following fields:
optional bool shell = 6 [default = true];
optional string value = 3;
repeated string arguments = 7;
There is some documentation for them which explains their behavior for the
command executor but not for the docker executor:
https://github.com/apache/mesos/blob/master/include/mesos/mesos.proto#L280
Both executors work fairly differently when you use shell=false and arguments.
For the command executor, executing "echo $PORT" withOUT variable substitution
could be achieved with shell=false value="/usr/bin/echo"
arguments=["/usr/bin/echo", "$PORT"]. See
https://github.com/apache/mesos/blob/0.22.1/src/launcher/executor.cpp#L245
For the docker executor, using the same arguments with the "ubuntu" image (no
default entrypoint) would result in executing "/usr/bin/echo /usr/bin/echo
$PORT" which is rather confusing. See
https://github.com/apache/mesos/blob/0.22.1/src/docker/docker.cpp#L451-L457
For the command executor, I would propose to emphasize that for all sane use
cases `arguments(0)` should be equal to `value` if you use shell = false.
It would also help to include some example, e.g.:
* Executing "python -m SimpleHTTPServer $PORT" with variable substitution =>
shell=true value="python -m SimpleHTTPServer $PORT", arguments are ignored
* Executing "echo $PORT" withOUT variable substitution => shell=false
value="/usr/bin/echo" arguments=["/usr/bin/echo", "$PORT"]
In the case of docker you actually need to distinguish between containers with
a default entrypoint and the ones without.
With the ubuntu image (without default endpoint) examples could be:
* Executing "python -m SimpleHTTPServer $PORT" with variable substitution =>
shell=true value="python -m SimpleHTTPServer $PORT", arguments are ignored
* Executing "echo $PORT" withOUT variable substitution => shell=false
value="/usr/bin/echo" arguments=["$PORT"] OR arguments=["/usr/bin/echo",
"$PORT"]
Thanks!
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