Function Compute:Configure instance health checks

Limitations

Health checks are supported only for Web Function and GPU functions.

How health checks work

Instance startup behavior

For instructions on how to set the Threshold for Successful Detections and Maximum Failures, see Configure health checks in the console.

Single health check behavior

Scheduling after a health check failure

Configure health checks in the console

This section explains how to configure health checks for a function. The example uses a Web Function with the Node.js 18 Runtime.

Step 1: Create a function

1. Log in to the Function Compute console, and in the left navigation bar, select Function Management > Functions.

2. In the top navigation bar, select a region. On the Functions page, click Create Function.

3. On the Create Function page, select Web Function. For Custom Runtime, select Custom Runtime. Then, click Create.

4. On the function details page, select the Code tab. Edit the function code in the code editor, and then click Deploy.

   The following is the sample code for index.js.

   'use strict';
   
   // Constants
   const PORT = 9000;
   const HOST = '0.0.0.0';
   const REQUEST_ID_HEADER = 'x-fc-request-id'
   
   const express = require('express');
   const bodyParser = require('body-parser');
   const app = express();
   
   app.use(bodyParser.urlencoded({ extended: true }));
   app.use(bodyParser.json());
   app.use(bodyParser.raw());
   
   app.get('/readyz', (req, res) => {
     console.log(`receive health check`);
     res.status(200);
     console.log(`i am ready`);
     res.send('i am ready\n');
   });
   
   // invocation
   app.post('/invoke', (req, res) => {
     var rid = req.headers[REQUEST_ID_HEADER]
     console.log(`FC Invoke Start RequestId: ${rid}`)
     res.send('OK');
     console.log(`FC Invoke End RequestId: ${rid}`)
   });
   
   var server = app.listen(PORT, HOST);
   console.log(`Running on http://${HOST}:${PORT}`);
   
   server.timeout = 0; // never timeout
   server.keepAliveTimeout = 0; // keepalive, never timeout

   In the code above, readyz is the health check handler. It processes HTTP GET requests sent to the /readyz path. After you complete Step 2: Configure health checks for the function instance, you can configure Function Compute to periodically run this handler to check instance health.

   When Function Compute determines that your function instance is unhealthy, it attempts to route requests to other healthy instances. If Function Compute fails to do so, it returns an error related to the health check failure.

Step 2: Configure health checks

1. Log on to the Function Compute console, and in the left navigation bar, select Function Management > Functions.

2. In the top navigation bar, select a region. On the Functions page, click the function that you created in the previous step.

3. On the function details page, select the Configuration tab. To the right of Advanced Settings, click Modify. In the Advanced Settings panel, enable the Health Check switch, configure the parameters as described in the following table, and then click Deploy.

   Parameter	Description
   Request Path	The path to which Function Compute sends an HTTP GET request to perform a health check. The value must start with /.
   Delay for First Detection	The delay in seconds after instance startup before the first health check runs.
   Detection Interval	The interval in seconds between health checks.
   Timeout Period	The timeout in seconds for a health check response. If a response is not received within this period, the check fails.
   Maximum Failures	The number of consecutive failed health checks before an instance is marked as unhealthy.
   Threshold for Successful Detections	The number of consecutive successful health checks required to mark an unhealthy instance as healthy again.

Step 3: Verify the health check

1. On the function configuration page, select the Code tab and click Test Function to view the result.

   With the sample code in Step 1, the function instance passes the health check and returns OK.

2. Replace the health check handler in the code with the following snippet. Click Deploy. After the code is deployed, click Test Function again to see the result.

   The modified code is as follows.

   app.get('/readyz', (req, res) => {
     console.log(`receive health check`);
     res.status(500);
     console.log(`i am not ready`);
     res.send('i am not ready\n');
   });

   The health check will now always fail with a 500 status code. When you invoke the function again, you will receive the following response:

   {
       "RequestId": "1-65081d42-e4895cbc7d6252bda643****",
       "Code": "FunctionNotStarted",
       "Message": "The function http server cannot be started. check function health failed with status code: 500 "
   }

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