Concurrency on Azure Functions (PHP) with custom handlers

PHP is not among supported languages in Azure Functions, but one can easily implement that with the help of Azure Functions custom handlers. There are several posts over the Internet guiding you how to set up a PHP Function with custom handlers, but one needs to pay attention to the concurrency here, or he/she may easily ends up with HTTP 500.121(Timeout).

 

Performance bottleneck

I created one PHP function app following the guidance from Internet, below is the host.json file. The HTTP trigger function is quite simple, it will only sleep 50 seconds once it is triggered before return. When I send 10 requests almost at the same time, the response time of each requests is increasing, until it reaches 230s(the maximum time IIS server on Azure App Service allowed) and returns HTTP 500.121(Timeout).

 

 

{
  "version": "2.0",
  "logging": {
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "excludedTypes": "Request"
      }
    }
  },
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[2.*, 3.0.0)"
  },
  "customHandler": {
    "description": {
      "defaultExecutablePath": "php",
      "workingDirectory": "",
      "arguments": [
        "-S",
        "127.0.0.1:%FUNCTIONS_CUSTOMHANDLER_PORT%",
        "router.php"
      ],
      "enableForwardingHttpRequest": true
    }
  }
}

 

 

Requests response time:

PreciseTimeStamp	Cs_method	Cs_uri_stem	S_port	Sc_status	Sc_substatus	Sc_win32_status	Time_taken(ms)
2021-09-27 06:28:45.1512587	GET	/api/function1	443	200	0	0	50027
2021-09-27 06:28:45.1722946	GET	/api/function1	443	200	0	0	73530
2021-09-27 06:29:45.1965994	GET	/api/function1	443	200	0	0	123586
2021-09-27 06:30:45.2202146	GET	/api/function1	443	200	0	0	173613
2021-09-27 06:31:45.2311004	GET	/api/function1	443	200	0	0	223630
2021-09-27 06:31:45.2390925	GET	/api/function1	443	500	121	0	230002
2021-09-27 06:32:45.3702086	GET	/api/function1	443	500	121	0	230001
2021-09-27 06:33:45.4016691	GET	/api/function1	443	500	121	0	230003
2021-09-27 06:34:45.4178058	GET	/api/function1	443	500	121	0	230005

 

Root Cause

If you get back and check my host.json again, you will notice that I am launching a PHP built-in web server with the help of Azure Functions custom handlers. The web server runs only one single-threaded process, so PHP applications will stall if a request is blocked.

 

 

php -S 127.0.0.1:%FUNCTIONS_CUSTOMHANDLER_PORT% router.php

 

 

One doc you may reference: 

https://www.php.net/manual/en/features.commandline.webserver.php

 

What I can do

• If one insists on using Azure Functions in his/her design, then he/she may leverage environmental variable ‘PHP_CLI_SERVER_WORKERS’ and set up a large number to achieve concurrency. This feature is only provided by PHP7.4 on linux. But PHP7.4 on linux is not available on current linux plan, one needs to run his/her function app in a custom linux container which has built that has PHP installed. Please note, even though it can achieve certain concurrency with multiple PHP processes, but it still not recommended to use in production environment due to limited performance.

Attach the Dockerfile below to your reference.

 

 

# To enable ssh & remote debugging on app service change the base image to the one below
FROM mcr.microsoft.com/azure-functions/dotnet:3.0-appservice 
ENV AzureWebJobsScriptRoot=/home/site/wwwroot \
    AzureFunctionsJobHost__Logging__Console__IsEnabled=true

#COPY --from=installer-env ["/home/site/wwwroot", "/home/site/wwwroot"]

RUN apt -y install lsb-release apt-transport-https ca-certificates 
RUN wget -O /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg
RUN echo "deb https://packages.sury.org/php/ $(lsb_release -sc) main" | tee /etc/apt/sources.list.d/php.list
RUN apt update && apt install php7.4 -y


COPY . /home/site/wwwroot

 

 

• The best option is to switch to PHP web app instead of Azure Functions with custom handler. In that way, the PHP module launched by Apache/Nginx server could handle the API requests concurrently.

 

Posted at https://sl.advdat.com/3ayhrlY