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<p class="MsoNormal"><span style="color:#1F497D">Hi Hung,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thank you for your advice that really sound like much simpler and better solution!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b>From:</b> nginx-devel <nginx-devel-bounces@nginx.org> <b>
On Behalf Of </b>Hung Nguyen<br>
<b>Sent:</b> Monday, February 18, 2019 3:52 PM<br>
<b>To:</b> nginx-devel@nginx.org<br>
<b>Subject:</b> Re: [Module development] Any good idea to hook response from proxy<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">As my understanding all you need is doing a body filter on backend_upstream response and send a set request to memcache with value is response itself. <span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">To determine whether response is from memcache or from backend, before proxy pass request to backend you can set some customize header like x-update-cache: true, inside the filter you check that header and perform
set operation. <o:p></o:p></p>
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<p class="MsoNormal">--<o:p></o:p></p>
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<p class="MsoNormal">Hưng<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><br>
On Feb 18, 2019, at 21:21, <<a href="mailto:Maciej.Grochowski@sony.com">Maciej.Grochowski@sony.com</a>> <<a href="mailto:Maciej.Grochowski@sony.com">Maciej.Grochowski@sony.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">At very beginning apologizes for the newbie question, but I am very new in Nginx but would like to extend some functionality in the existing module.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">I am currently using ngx_http_enhanced_memcached_module, and it meets most of my needs.
<o:p></o:p></p>
<p class="MsoNormal">However, currently, I need to manually populate cache, via PUT requests.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">My nginx configuration looks as follow:<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">```<o:p></o:p></p>
<p class="MsoNormal">upstream memcached_upstream {<o:p></o:p></p>
<p class="MsoNormal"> server 127.0.0.1:11211;<o:p></o:p></p>
<p class="MsoNormal"> keepalive 20;<o:p></o:p></p>
<p class="MsoNormal">}<o:p></o:p></p>
<p class="MsoNormal">upstream backendstorage_upstream {<o:p></o:p></p>
<p class="MsoNormal"> server 10.0.0.10:9000<o:p></o:p></p>
<p class="MsoNormal">}<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">server {<o:p></o:p></p>
<p class="MsoNormal"> location / {<o:p></o:p></p>
<p class="MsoNormal"> error_page 404 502 504 = @fallback;<o:p></o:p></p>
<p class="MsoNormal"> error_page 405 = 200 $uri;<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"> set $enhanced_memcached_key "$request_uri";<o:p></o:p></p>
<p class="MsoNormal"> ...<o:p></o:p></p>
<p class="MsoNormal"> enhanced_memcached_pass memcached_upstream;<o:p></o:p></p>
<p class="MsoNormal"> }<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"> location @fallback {<o:p></o:p></p>
<p class="MsoNormal"> proxy_pass <a href="http://backendstorage_upstream">
http://backendstorage_upstream</a>;<o:p></o:p></p>
<p class="MsoNormal"> }<o:p></o:p></p>
<p class="MsoNormal">}<o:p></o:p></p>
<p class="MsoNormal">```<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">I started thinking of embedding STORE functionality inside the module itself. A high-level idea would be:<o:p></o:p></p>
<p class="MsoNormal">whenever we got cache miss to fetch the response from backend_upstream via `proxy_pass` and then get response and
<o:p></o:p></p>
<p class="MsoNormal">sent it back to the `memcached_upstream` via PUT method.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">This sounds really simple, however, I have 2 questions based on my understanding of Nginx internals:<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">1. `proxy_pass` is a method which runs inside NGX_HTTP_CONTENT_PHASE, so based on documentation only one method in that type can be inside the location.<o:p></o:p></p>
<p class="MsoNormal">In order to hijack response from `proxy_pass`, the only way that I can see is to wrap `proxy_pass` via i.e. `enhanced_memcached_proxy_pass`.
<o:p></o:p></p>
<p class="MsoNormal">In that custom method: first of all original code from proxy module would be run and then as one of the end stages, a custom method like (i.e. input_filter) would be able to access response from the backend and send content to Memcached.<o:p></o:p></p>
<p class="MsoNormal">Given the size of the proxy module and its implementation based on callbacks, first thoughts that I have is that I can end up easily via merging these modules.<o:p></o:p></p>
<p class="MsoNormal">Is there any other easier way to access the response from location?<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">2. If I will need to implement such a method like `enhanced_memcached_proxy_pass`, is there any recommended (asynchronous) way to send PUT to external service.<o:p></o:p></p>
<p class="MsoNormal">My understanding is that as long as we spent time doing operations inside pipeline we block particular event which can cause delay to the client (of course here I would like to send response first to the client and then store it).<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Thank you for any help!<o:p></o:p></p>
<p class="MsoNormal">Maciej<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman",serif">_______________________________________________<br>
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