We are actually testing "Attach Docker container" wich seems to be a solution. But, in the documentation of the plugin, this functionnality is marked as experimental. Is this still the case ?

You can follow this issue on github : Issue #757

I close this issue related to jenkinsci/docker-plugin#757

For those of us that do want to use JNLP rather than Attach mode, here is a quick and dirty workaround that has proven to stabilize docker launching under heavy load (in my case, a matrix job spawning 70 containers simultaneously).  All it does is re-run the JNLP script a few times in case the master wasn't ready.  Without this, I was left with a ton of stopped containers and no resources.

I simply change the ENTRYPOINT in my images from the default (/usr/local/bin/jenkins-agent script from jenkins/jnlp-slave) to this script:

#!/bin/bash

ACTUAL_ENTRYPOINT=/usr/local/bin/jenkins-slave
# sleep between retries, if needed (s)
SLEEP=${JNLP_RETRY_SLEEP:-5}  
# Try to reconnect this many times
TRIES=${JNLP_RETRY_COUNT:-3}
# Stop retrying after this many seconds regardless
MAXTIME=${JNLP_RETRY_MAXTIME:-60}

# Do not retry if we're running bash to debug in this container
# more than 1 arg is probably jenkins jnlp start
if [ $# -eq 1 ] ; then
  exec $*
fi

START=$(date +%s)
while [ $TRIES -gt 0 ] && [ $(($(date +%s) - $START)) -lt $MAXTIME ] && ! $ACTUAL_ENTRYPOINT "$@" ; do
  CODE=$?
  echo "$ACTUAL_ENTRYPOINT exited [$CODE], waiting $SLEEP seconds and retrying"
  sleep $SLEEP
  TRIES=$(($TRIES - 1))
done

echo "Exiting [$CODE] with $TRIES remaining tries and $(($(date +%s) - $START)) seconds elapsed"

exit $CODE

and my Dockerfile looks like this:

FROM jenkins/jnlp-slave # directly or indirectly
CMD [ "/bin/bash" ]
ENTRYPOINT [ "entrypoint" ]

(My images have bash... for alpine you may want to change the shebang to /bin/sh)

For the record, network stability has been an issue for me with Attach.  Since I'm using classic Swarm, the topology is too complex and the connection is sometimes lost:

Master -> Swarm Manager -> Docker Host -> Container

With JNLP, it's simply:

Container -> Master

oleg_nenashev, perhaps it may be worthwhile to integrate some (better than the above) retry logic in jenkins-agent script or even slave.jar itself?  (possibly after identifying the "unknown name" error from the master).   Happy to make a PR with some guidance.

Personally, I approve of adding retry logic to pretty-much anything network related. The SSH connection mechanism from Master -> Slave-Node has lots of (configurable) retry logic so there is "prior art" to having this.

There's a lot of chicken/egg issues when it comes to starting Jenkins slaves and so it makes a lot of sense to ensure that no aspect of this delicate negotiation process requires things to happen in a specific order.
e.g. in the docker-plugin's case, it wants to know the container-ID of the container (which is only available once the "run container" command has returned) to write into the slave node instance before returning it to Jenkins, so it has to start the container before Jenkins gets it ... but if the slave container starts up very quickly then Jenkins might well receive and reject its connection request before Jenkins adds the node to its list of permitted slaves.
A retry mechanism would allow an easy workaround for this ... as well as helping with situations where the network between the master and slave is less than perfect.
FYI the script I use for starting Windows VMs with the vSphere-plugin (linked to from the vSphere plugin's wiki page) that connect via JNLP contains a lot of retry logic and that's proved its worth many times over.

What I would recommend, however, is that the number of retries and the delay between retries be made configurable.
...and I'd also recommend that

$ACTUAL_ENTRYPOINT $*

should be changed to

${ACTUAL_ENTRYPOINT} "$@"

so whitespace in arguments gets preserved (something that'd be less of an issue if this retry logic was incorporated in the core /usr/local/bin/jenkins-slave script).

Completely agree, pjdarton.

The above was meant to be an example of a quick-and-easy fix for my use, not a polished product.   Once we get into command-line args territory there is an increase in complexity (like shifting bash args).  Currently (with the script behavior hardcoded) I can simply substitute my images in both k8s and docker jenkins plugins, without manually configuring entrypoint command-line args in the UI (using implicit defaults).  

So basically we agree that this logic would ideally be part of the jnlp image components.

Fair point about spaces, I'll edit my code above.

Note: $@ not $*
FYI

"$*"

will glob all CLI arguments into one argument, which is pretty-much guaranteed to break things (it'll break things if more than one argument was provided), whereas

$*

would only break things if folks provided arguments containing whitespace.

"$@"

is the best option when you want to "pass through all arguments as they were provided".

TL;DR: Whitespace in arguments is very easy to get wrong

Thanks pjdarton for the reminder.  I also added rudimentary configuration for sleep/etc via environment variables.

Hi,

Thank akom for the retry bit, we tried it on our end to secure the jnlp connexion. The retry in itself seems to work great, but since we implemented it, our containers doesn't end properly:

The kill -15 sent on job termination is not correctly interpreted by the container, and we have to wait 10 sec for a kill -9 to really put an end to the container.

This is problematic because we have a small window where the master believe the container (and the agent related) is free to use. It could then try to start a job in it, with no chance to last long.

What I could figure out is that since the entrypoint is the new script, when the $ACTUAL_ENTRYPOINT run, it is not the PID 1, and the jar is not linked to our new entrypoint (since is it started by exec command).

When the kill -15 occur, not every process are killed, so the container stays alive.

I tried to add the exec command before runnning the $ACTUAL_ENTRYPOINT, it resolve the issue of the sigterm interpretation, but we loose the retry logic...

I'm still trying to figure out a solution to torward properly sigterms and keep the retry.

Hello,

Here's an update regarding the issue between sigterm propagation and retry :

We managed to make them work together following this article: https://unix.stackexchange.com/questions/146756/forward-sigterm-to-child-in-bash

Instead of using the exec command, we used wait and trap commands to meet our need. I find the Article from Andreas Veithen++ to be very interesting and detailed.

We put back the "usual" jenkins entrypoint in the dockerfile, but instead of starting the jar, it launch our script :

exec $JAVA_BIN $JAVA_OPTS $JNLP_PROTOCOL_OPTS -cp /usr/share/jenkins/agent.jar hudson.remoting.jnlp.Main -headless $TUNNEL $URL $WORKDIR $DIRECT $PROTOCOLS $INSTANCE_IDENTITY $OPT_JENKINS_SECRET $OPT_JENKINS_AGENT_NAME "$@"

replaced by :

exec /usr/local/bin/jenkins-agent-retry.sh "$@"

Here is what jenkins-agent-retry.sh look like now :

#!/usr/bin/env sh

if [ $# -eq 1 ]; then
    # if `docker run` only has one arguments, we assume user is running alternate command like `bash` to inspect the image
    exec "$@"
fi


# Gestion SIGTERM https://unix.stackexchange.com/questions/146756/forward-sigterm-to-child-in-bash
prep_term()
{
    unset term_child_pid
    unset term_kill_needed
    trap 'handle_term' TERM INT
}

handle_term()
{
    if [ "${term_child_pid}" ]; then
        kill -TERM "${term_child_pid}" 2>/dev/null
    else
        term_kill_needed="yes"
    fi
}

wait_term()
{
    term_child_pid=$!
    if [ "${term_kill_needed}" ]; then
        kill -TERM "${term_child_pid}" 2>/dev/null 
    fi
    wait ${term_child_pid}
    trap - TERM INT
    wait ${term_child_pid}
}

echo "[INFO] JDK $($JAVA_BIN -version 2>&1|awk '$0~/openjdk version/ {print $3}') to connect to master"
echo "[INFO] Remoting Version: $($JAVA_BIN -cp /usr/share/jenkins/agent.jar hudson.remoting.jnlp.Main -headless -version)"
echo "[INFO] Start Agent command: " $JAVA_BIN $JAVA_OPTS $JNLP_PROTOCOL_OPTS -cp /usr/share/jenkins/agent.jar hudson.remoting.jnlp.Main -headless $TUNNEL $URL $WORKDIR $DIRECT $PROTOCOLS $INSTANCE_IDENTITY $OPT_JENKINS_SECRET $OPT_JENKINS_AGENT_NAME "$@"

# Gestion Retry from https://issues.jenkins-ci.org/browse/JENKINS-59790?focusedCommentId=379913&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-379913
SLEEP=${JNLP_RETRY_SLEEP:-5}
# Try to reconnect this many times
TRIES=${JNLP_RETRY_COUNT:-3}
# Stop retrying after this many seconds regardless
MAXTIME=${JNLP_RETRY_MAXTIME:-60}

START=$(date +%s)
while [ $TRIES -gt 0 ] && [ $(($(date +%s) - $START)) -lt $MAXTIME ]; do
    prep_term
    $JAVA_BIN $JAVA_OPTS $JNLP_PROTOCOL_OPTS -cp /usr/share/jenkins/agent.jar hudson.remoting.jnlp.Main -headless $TUNNEL $URL $WORKDIR $DIRECT $PROTOCOLS $INSTANCE_IDENTITY $OPT_JENKINS_SECRET $OPT_JENKINS_AGENT_NAME "$@" &
    wait_term
    CODE=$?
    if [ $CODE -eq 143 ]; then
        break
    fi
    echo "exited [$CODE], waiting $SLEEP seconds and retrying"
    sleep $SLEEP
    TRIES=$(($TRIES - 1))
done

Note to anyone monitoring this: There's a prospective fix here - https://github.com/jenkinsci/docker-plugin/pull/789
However, it needs to be tested.
I don't have this problem in my docker environment so I can't test it; what I need is someone who can reproduce the issue to try a "without this fix" and a "with this fix" comparison and to report back (to the conversation in the PR as I don't have the time to monitor stuff in JIRA as closely as I should).

If I can get a decent level of confidence that this change does actually fix the problem then I'll merge it in and push out a maintstream release with the fix.

Fixed by https://github.com/jenkinsci/docker-plugin/pull/789 which has (just) been merged and will be in the next release.