Rails app may be crashing passenger, not sure how to debug? - ruby-on-rails

My app generates some image data on the fly and sends it back to the browser with send_data some_huge_blob, :type => 'image/png'. This works well enough in development mode, but in production with nginx/passenger in the mix it appears as if sometimes passenger just crashes. Here is the debug output in my nginx log
[ pid=596 thr=140172782794496 file=ext/common/ApplicationPool/Pool.h:1162 time=2011-07-25 23:15:14.965 ]: Exception occurred while connecting to checked out process 1428: Cannot connect to Unix socket '/tmp/passenger.1.0.589/generation-0/backends/ruby.kJRjXYuZteKoogZIufN8a2cDPdpbIlYmIr1hh3G9UV7GhKDB4pqZ5y0jR': Connection refused (111)
[ pid=596 thr=140172782794496 file=ext/common/ApplicationPool/Pool.h:685 time=2011-07-25 23:15:14.965 ]: Detaching process 1428
[ pid=596 thr=140172782794496 file=ext/common/ApplicationPool/../Process.h:138 time=2011-07-25 23:15:14.969 ]: Application process 1428 (0x2676ee0): destroyed.
[ pid=1405 thr=70178806733240 file=abstract_request_handler.rb:466 time=2011-07-25 23:15:14.982 ]: Accepting new request on main socket
2011/07/25 23:15:16 [error] 642#0: *96 upstream prematurely closed connection while reading response header from upstream, client: 173.8.216.57, server: app.somedomain.com, request: "GET /projects/4e2dee4c106a821bf2000008/revisions/1/assets/Layout2.psd/preview HTTP/1.1", upstream: "passenger:unix:/passenger_helper_server:", host: "app.somedomain.com"
Note that there is nothing in my production.log file that indicates the request even makes it to the app!
Any ideas? Or ideas as to how to debug this further? The connection refused bit is interesting...
For what it's worth, this is an Ubuntu image on a micro instance in AWS.

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Also, my browser will try to load the page for some time, and then show a blank page, with the response header giving a 500.
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E, [2014-09-24T21:22:33.505511 #18252] ERROR -- : app error: invalid byte sequence in UTF-8 (ArgumentError)
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I am trying to configure nginx for a rails app on DigitalOcean. When I open my IP, I see the BAD GATEWAY (502) message.
In logs is
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What does error message means and how could I fix it?
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EDIT:
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/home/deployer/apps/myproject-staging
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Why am I getting a segmentation fault in Typheous when I perform a POST request?

It's really tricky in our production environment( Red Hat Enterprise Linux Server release 5.4 (Tikanga) and curl 7.15.5 (x86_64-redhat-linux-gnu) libcurl/7.15.5 OpenSSL/0.9.8b zlib/1.2.3 libidn/0.6.5) that the POST request become to GET request automatically. Below is the relative log provide by nginx.
cache: [GET /login] miss
url->http://localhost:8080/login
About to connect() to localhost port 8080
Expire at 1339680839 / 265363 (300000ms)
Trying 127.0.0.1... * connected
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In our development environment( which is Ubuntu12.04 and curl 7.22.0 (x86_64-pc-linux-gnu) libcurl/7.22.0 OpenSSL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3), everything goes ok.
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After I upgraded the curl from 7.15 to 7.22. The problem has been solved.

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Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
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More information about this error may be available in the server error log.
Apache/2.2.16 (Ubuntu) Server at localhost Port 80
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[Thu Dec 01 16:55:23 2011] [error] [client 127.0.0.1] Premature end of script headers: view_transactions, referer: http://localhost/admin_portal/1014978061/view_transactions
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[ pid=796 thr=-608495398 file=utils.rb:176 time=2011-12-01 11:25:23.878 ]: *** Exception NoMethodError in application (undefined method `new' for Rails:Module) (process 796, thread #<Thread:0xb77631b4>):
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from /home/brijendra/aptana_studio_3_workspace/wantsa/vendor/plugins/newrelic_rpm/lib/new_relic/agent.rb:167:in `logger'
I would be eager to post any other output if required and also suggestions to fix this issue.
I fixed this error by changing cache as true in my development.rb and it worked fine.

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