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Message-ID: <5201C46F.8060303@christopherschultz.net>
Date: Tue, 06 Aug 2013 23:52:15 -0400
From: Christopher Schultz <chris@christopherschultz.net>
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To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: [OT] Using the bin/daemon.sh script on ubuntu.
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Igor,

On 8/6/13 6:28 AM, Igor Cicimov wrote:
> On 06/08/2013 12:40 AM, "Jeffrey Janner"
> <Jeffrey.Janner@polydyne.com> wrote:
>> 
>>> -----Original Message----- From: Christopher Schultz
>>> [mailto:chris@christopherschultz.net] Sent: Friday, August 02,
>>> 2013 10:30 PM To: Tomcat Users List Subject: Re: [OT] Using the
>>> bin/daemon.sh script on ubuntu.
>>> 
>>> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256
>>> 
>>> Christian
>>> 
>>> On 8/1/13 11:55 AM, Christian Schneider wrote:
>>>> On our (AWS) installation we have limited space on /opt,
>>>> therefore we attached an EBS volume  to /var/, - otherwise we
>>>> would get problems with the log files. Now it can grow above
>>>> some GB.
>>> 
>>> Have you thought about using /mnt/ephemeral[0-9]?
>>> 
>>> Our instances have ~1TiB in combined ephemeral storage
>>> available per instance. I'm sure it depends upon the instance
>>> type, though. Remember that terminating the instance loses the
>>> ephemeral data.. that's what makes it ... ephemeral. Just
>>> remember to copy what you need back to an EBS-backed storage
>>> volume before you terminate.
>>> 
>>> - -chris
>> 
>> Chris, If I remember my empirical testing of the AWS ephemeral
>> storage system, you actually lose data on shutdown, not
>> termination.
> 
> Not true, the ephemeral data is only lost on instance termination.

Confirmed -- at least with "shutdown -r", and on an m1.large instance
- -- /mnt/ephemeralX retains files across reboots. I didn't do a "stop"
and "start" from the GUI or anything like that, though.

I think you're supposed to be able to rely on ephemeral storage. The
thing is that it's not EBS-backed: it's actually only on the physical
server that you get when you launch an instance. When you shut-down,
the data stays on the physical machine and you can only get to it
again when you boot the same instance on the same machine. Since AWS
always runs instances on the same physical hardware every time, you're
good unless you /terminate/ (i.e. discard) the instance.

Honestly, I was a bit surprised to find out that each time you launch
an instance it doesn't just get launched on some random piece of
equipment. That would seem more flexible (if wasteful: moving GiBs of
data around to various hosts isn't exactly fast) to me.

On more than one occasion, I've had an instance start acting funny and
shortly thereafter, I get an email from AWS saying that they will be
terminating my instance in a few days. You can't just "migrate" the VM
to another piece of hardware. Instead, you have to image the VM,
create an AMI from that image, create a new instance with that AMI,
and destroy the old instance. (Then delete the old image *and* EBS
store, otherwise you continue to pay for the disk space taken up by an
instance that will never again be launched). Pain in the neck.

I think you can create an AMI directly from a running instance these
days (probably for this exact reason).

- -chris
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