<h1 dir="auto">Checklist</h1>

<ul class="contains-task-list">
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have checked the <a href="https://github.com/celery/celery/issues?utf8=%E2%9C%93&amp;q=is%3Aissue+label%3A%22Issue+Type%3A+Feature+Request%22+">issues list</a><br>
for similar or identical feature requests.</li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have checked the <a href="https://github.com/celery/celery/pulls?utf8=%E2%9C%93&amp;q=is%3Apr+label%3A%22PR+Type%3A+Feature%22+">pull requests list</a><br>
for existing proposed implementations of this feature.</li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have checked the <a href="https://github.com/celery/celery/commits/master">commit log</a><br>
to find out if the if the same feature was already implemented in the<br>
master branch.</li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have included all related issues and possible duplicate issues<br>
in this issue (If there are none, check this box anyway).</li>
</ul>
<h2 dir="auto">Related Issues and Possible Duplicates</h2>

<h4 dir="auto">Related Issues</h4>
<ul dir="auto">
<li>None</li>
</ul>
<h4 dir="auto">Possible Duplicates</h4>
<ul dir="auto">
<li>None</li>
</ul>
<h1 dir="auto">Brief Summary</h1>
<p dir="auto">Forgive me if this is already trivially possible, but the <a href="http://docs.celeryproject.org/en/latest/tutorials/task-cookbook.html#ensuring-a-task-is-only-executed-one-at-a-time" rel="nofollow">docs</a> suggest it isn't.</p>
<p dir="auto">For the simplest case, it would be nice to have an option to not allow tasks to overlap per worker i.e. where by <em>simplest case</em> I mean a single instance with one worker running <em>Periodic Tasks</em> for example (non-distributed)</p>
<h1 dir="auto">Design</h1>
<h2 dir="auto">Architectural Considerations</h2>
<p dir="auto">Current behavior would remain default</p>
<h2 dir="auto">Proposed Behavior</h2>
<p dir="auto">Each worker checks if the task is already running on itself. Exponential backoff comes free?</p>
<h2 dir="auto">Proposed UI/UX</h2>
<ul dir="auto">
<li>Checkbox on django-celery-beat admin maybe?</li>
</ul>
<h2 dir="auto">Diagrams</h2>

<p dir="auto">N/A</p>
<h2 dir="auto">Alternatives</h2>
<p dir="auto">Implement locking as per <a href="http://docs.celeryproject.org/en/latest/tutorials/task-cookbook.html#ensuring-a-task-is-only-executed-one-at-a-time" rel="nofollow">http://docs.celeryproject.org/en/latest/tutorials/task-cookbook.html#ensuring-a-task-is-only-executed-one-at-a-time</a>, a heavy burden compared to the proposal.</p>
<h1 dir="auto">Checklist</h1>

<ul class="contains-task-list">
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have checked the <a href="https://github.com/celery/celery/issues?utf8=%E2%9C%93&amp;q=is%3Aissue+label%3A%22Category%3A+Documentation%22+">issues list</a><br>
for similar or identical bug reports.</li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have checked the <a href="https://github.com/celery/celery/pulls?q=is%3Apr+label%3A%22Category%3A+Documentation%22">pull requests list</a><br>
for existing proposed fixes.</li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have checked the <a href="https://github.com/celery/celery/commits/master">commit log</a><br>
to find out if the bug was already fixed in the master branch.</li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have included all related issues and possible duplicate issues in this issue<br>
(If there are none, check this box anyway).</li>
</ul>
<h2 dir="auto">Related Issues and Possible Duplicates</h2>

<h4 dir="auto">Related Issues</h4>
<ul dir="auto">
<li>None</li>
</ul>
<h4 dir="auto">Possible Duplicates</h4>
<ul dir="auto">
<li>None</li>
</ul>
<h1 dir="auto">Description</h1>

<p dir="auto">The "first-steps-with-celery" advises to use the following docker command to start RabbitMQ instance:</p>
<p dir="auto">docker run -d -p 5462:5462 rabbitmq</p>
<p dir="auto">However this won't work, as the default port for rabbit is 5672, not 5462.</p>
<h1 dir="auto">Suggestions</h1>

<p dir="auto">replace 5462 with 5672.</p>