Re: [Proposal] Wanted a Babysitter for my applicatoin. ; -)

Amit Kumar Gupta

Hey Dhilip,

To clarify, we don't have a copy of executor for each garden-linux
container. A single "cell" VM has one executor, one garden-linux, and many
containers. The executor runs one monitor or "babysitter" process per each

What would be the benefit of running a monitor inside external systems
which report to the HM? With Diego, there is no HM, so who exactly would
it report to? And whatever it reports to, what can it do with that
information? The Diego system components can take action when hearing
about a failed container running in a Diego cell, it can schedule the
process to be restarted, or whatever the right action may be given the
crash restart policies. How can Diego or any Cloud Foundry component take
action against an external system?

I think you highlight something valuable, that it would be nice for the
platform to support running things other than apps, e.g. a MySQL database.
The plan is that this can be solved within Diego's abstractions of tasks
and LRPs, and it's true for perhaps most stateless non-app workloads, but
things like databases are still hard, due to persistence being a hard
problem. If you have not already seen it, Ted Young and Caleb Miles talk
at the last CF Summit about this problem is a good one to watch:

Not all containers run sshd. Typically, the CC is responsible for
requesting that an LRP have SSH access enabled, it's not conflated with
Diego's responsibilities. It's also optional for the CC, users and space
managers can opt to disable SSH (actually, I believe it's disabled by


On Mon, Oct 5, 2015 at 10:39 PM, Dhilip Kumar S <dhilip.kumar.s(a)>

Hi All,

Thanks for the response.

Hi Amit,

Thanks for the info, I haven’t noticed that we run a copy of executor for
each ‘garden-linux’ container that we launch. We do have a ‘push’ based
container metrics collection and monitoring mechanism already in place
then, In this case I can think of only the following benefits here.

1) This can become a unified health check approach as this binary
can be packed within the container, it can even run inside a
docker-container of an external system and keep pushing to a common HM. Or
we could run this in the same VM as a My-SQL instance to get its health.

2) This can be a part of the SshD as we are running a daemon in
every container anyways.

Ofcourse the original intention is to see if we could slightly alter the
way diego’s monitoring/metrics collection works. If this is already
implemented then I do not see a point perusing this idea.

Thanks for your time CF,


*From:* Amit Gupta [mailto:agupta(a)]
*Sent:* Tuesday, October 06, 2015 1:05 AM
*To:* Discussions about Cloud Foundry projects and the system overall.
*Cc:* Vinay Murudi; Krishna M Kumar; Liangbiao; Srinivasch ch
*Subject:* [cf-dev] Re: Re: [Proposal] Wanted a Babysitter for my
applicatoin. ;-)

I'm not sure I see the benefit here.

Diego, for instance, runs a customizable babysitter alongside each app
instance, and kills the container if the babysitter says things are going
bad. This triggers an event that the system can react to, and the system
also polls for container states because events can always be lost.

One thing to note is in this case, "the system" is the Executor, not HM9k
(which doesn't exist in Diego), or the Converger (Diego's equivalent of
HM9k), or Firehose or Cloud Controller which are very far removed from the
container backend. In Diego, the pieces are loosely coupled, events/data
in the system don't have to be sent through several layers of abstraction.



On Mon, Oct 5, 2015 at 10:09 AM, Curry, Matthew <Matt.Curry(a)>

We have been talking about something similar that we have labeled the
Angry Farmer. I do not think you would need an agent. The firehose and
cloud controller should have everything that you need. Also an agent does
not give you the ability to really measure the performance of instances
relative to each other which is a good indicator of bad state or


*From: *Dhilip Kumar S <dhilip.kumar.s(a)>
*Reply-To: *"Discussions about Cloud Foundry projects and the system
overall." <cf-dev(a)>
*Date: *Monday, October 5, 2015 at 9:31 AM
*To: *"Discussions about Cloud Foundry projects and the system overall." <
*Cc: *Vinay Murudi <vinaym(a)>, Krishna M Kumar <
krishna.m.kumar(a)>, Liangbiao <rexxar.liang(a)>,
Srinivasch ch <>
*Subject: *[cf-dev] [Proposal] Wanted a Babysitter for my applicatoin. ;-)

Hello CF,

Greetings from Huawei. Here is a quick idea that came up to our mind
recently. Honestly we did not spend enormous time brainstorming this
internally, but we thought we could go ahead and ask the community
directly. It would be a great help to know if such an idea had already been
considered and dropped by the community.

*Proposal Motivations*

The way health-check process is currently performed in cloud foundry is to
run a command
periodically; if the exit status is non-zero then it is assumed that an
application is non-responsive. We periodically repeat this process for all
the applications. Which means that we actually scan the entire data center
frequently to find one or few miss-behaving apps?

Why can’t we change the way health-check is done? Can it reflect the
real-world? The hospitals don’t periodically scan the entire community
looking for sick residents. Similarly, why can’t we report problems as and
when they occur – just like the real-world?

How about a lightweight process that constantly monitors the application’s
health and periodically reports in case an app is down or non-responsive
etc. In a huge datacenter where thousands of apps are hosted, and each app
has many instances. Wouldn’t it be better to make the individual
app/container come and tell us(healthmanager) that there is a problem
instead of scanning all of them? *Push versus Pull model* - Something
like a babysitter residing within each container and taking care of the
‘app’ hosted by our customers.

*How to accomplish this?*

Our proposal is for BabySitter(BS) – an agent residing within each
container optionally deployed using app-specific configuration. This agent
sends out the collected metrics to health monitor in case of any anomaly –
periodic time-series information etc. The agent should remember the
configured threshold value that each app should not exceed; otherwise it
triggers an alarm automatically to the health monitor in case of any
threshold violations. The alarm even could be sent many times a second to
the healthmonitor depending on the severity of the event, but the regular
periodic ‘time-series’ information could be collected every second but sent
once a minute to the HM. The challenge is design the application ‘bs’ as
lightweight as possible.

This is our primary idea, we also thought it would make more sense if we
club few more capabilities to babysitter like sshd (as a goroutine) and
fileserver(as a goroutine) but before we bore you with all that details, we
first want to understand what CF community thinks about this initial idea.

Thanks in advance,


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