[erlang-questions] upgrade path from R14B02 to OTP 17.5

[Garrett Smith]

Hi Luc,

I'd like to point out that today I am top posting, because some topics
should never die.

I would strongly suggest that you follow Fred's advice and setup a
second production server - not necessarily a separate machine/VM, but
a separate version of your app, in production. Then route a controlled
percentage of traffic to the new server and gradually increase that
over time as your confidence soars!

I honestly can't see this going well for you if you don't, short of
great luck or moments of sheer terror as things mysteriously break and
you scramble to revert to the old platform. Don't assume that
reverting will go smoothly - many famous outages occurred when a
backup procedure failed. I personally would just refuse to make such a
large change in production without a real mitigation strategy.

This is a fancier version of blue/green where you run two independent
services in parallel and gradually shift traffic/load to another
server, or back, as you carefully watch error rates.

This could require some application code change, or simply the
addition of a simple-as-possible router that lives in the app that
directs requests to one of the available back end apps. You should
also invest in some metrics - in particular error counts and
user-facing latencies (e.g. response times).

Again, you can run these on a single machine. The point here isn't
availability, but risk mitigation of large changes. Of course you can
distribute these apps on multiple servers if you want, but I wouldn't
jump into that before you see the rolling release process working
smoothly on your own machine with two Erlang VMs running locally.

You might get some push back from authority figures that this approach
is overkill - just "do it and get it over with - sure it's painful,
but this will buy us another six years!"

That's an argument, for sure, but consider the ongoing benefits of
having a 100% safe outlet for future changes - refactoring, features,
version revs, A/B testing etc. This app running on Windows would
become a model for others to follow!

This sounds really great to me - I would take the time you've budgeted
for reading README and work on this :)

Garrett

On Mon, Jun 15, 2015 at 6:25 PM, Tanguay, Luc (A584369)
<luc.tanguay@REDACTED> wrote:
> Hi.
>
>
>
> We have a Erlang/OTP distributed system running on R14B02 Windows 2008
> (32-bit).  We plan to upgrade to OTP 17.5 (64-bit).   The system involves
> one big server that distribute files to up to 40 smaller clients, three OTP
> applications, many TCP links between server and clients, a small mnesia
> database, many calls to erlang:open_port/2 to execute native Windows
> programs, etc.
>
>
>
> What is the safest upgrade path?  Go straight to OTP 17.5 or something else.
> Do I have to read all READMEs from R14B03 to OTP 17.5?
>
>
>
> Thanks,
>
> Luc
>
>
>
> ---
>
> Luc Tanguay, ing./P. Eng.
> Bell Canada
> 514-786-6440
> cell: 514-229-7585
>
>
>
>
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