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0.3.1 • Public • Published

Failure injection for Azure Functions - failure-azurefunctions


failure-azurefunctions is a small Node module for injecting failure into Azure Functions (https://azure.microsoft.com/en-us/services/functions/). It offers a simple failure injection wrapper for your Azure Function handler where you then can choose to inject failure by setting the failureMode to latency, exception, denylist, diskspace or statuscode. You control your failure injection using Key Vault.

How to install

  1. Install failure-azurefunctions module using NPM.
npm install failure-azurefunctions
  1. Add the module to your Azure function code.
const failureAzureFunctions = require('failure-azurefunctions')
  1. Wrap your handler.
exports.handler = failureAzureFunctions(async (event, context) => {
  1. Create a resource group and key vault (or skip to use existing one).
az group create --name <resource-group-name> -l "EastUS"
az keyvault create --name <your-unique-keyvault-name> -g <resource-group-name>
  1. Create a service principal.
az ad sp create-for-rbac --sdk-auth
  1. Give the service principal access to your key vault
az keyvault set-policy -n <your-unique-keyvault-name> --spn <clientId-of-your-service-principal> --secret-permissions delete get list set --key-permissions decrypt encrypt get list unwrapKey wrapKey
  1. Create a secret in Key Vault.
{"isEnabled": false, "failureMode": "latency", "rate": 1, "minLatency": 100, "maxLatency": 400, "exceptionMsg": "Exception message!", "statusCode": 404, "diskSpace": 100, "denylist": ["*.documents.azure.com"]}
az keyvault secret set --name <your-secret-name> --vault-name <your-unique-keyvault-name> --value "{\`"isEnabled\`": false, \`"failureMode\`"\`"latency\`"\`"rate\`": 1, \`"minLatency\`": 100, \`"maxLatency\`": 400, \`"exceptionMsg\`"\`"Exception message!\`"\`"statusCode\`": 404, \`"diskSpace\`": 100, \`"denylist\`": [\`"*.documents.azure.com\`"]}"
  1. Add environment variables to your Azure Function with values from above.
az functionapp config appsettings set --name <function-app-name> \
--resource-group <resource-group-name> --settings AZURE_CLIENT_ID=<your-clientID> AZURE_CLIENT_SECRET=<your-clientSecret> AZURE_TENANT_ID=<your-tenantId> KEY_VAULT_NAME=<your-unique-keyvault-name> FAILURE_INJECTION_PARAM=<your-secret-name>
  1. Try it out!


Edit the values of your secret in Key Vault to use the failure injection module.

  • isEnabled: true means that failure is injected into your Azure function.
  • isEnabled: false means that the failure injection module is disabled and no failure is injected.
  • failureMode selects which failure you want to inject. The options are latency, exception or statuscode as explained below.
  • rate controls the rate of failure. 1 means that failure is injected on all invocations and 0.5 that failure is injected on about half of all invocations.
  • minLatency and maxLatency is the span of latency in milliseconds injected into your function when failureMode is set to latency.
  • exceptionMsg is the message thrown with the exception created when failureMode is set to exception.
  • statusCode is the status code returned by your function when failureMode is set to statuscode.
  • diskSpace is size in MB of the file created in tmp when failureMode is set to diskspace.
  • denylist is an array of regular expressions, if a connection is made to a host matching one of the regular expressions it will be blocked.


In the subfolder example is a simple function which can be installed in Azure and used for test.


Inspired by Yan Cui's articles on latency injection for AWS Lambda (https://hackernoon.com/chaos-engineering-and-aws-lambda-latency-injection-ddeb4ff8d983) and Adrian Hornsby's chaos injection library for Python (https://github.com/adhorn/aws-lambda-chaos-injection/).


2020-10-23 v0.3.1

  • Change mitm mode back to connect to fix issue with all connections being blocked.

2020-08-24 v0.3.0

  • Changed mitm mode from connect to connection for quicker enable/disable of failure injection.
  • Renamed block list failure injection to denylist (breaking change for that failure mode).
  • Updated dependencies.

2020-02-28 v0.2.0

  • Fixed Key Vault integration.
  • Added simple example.
  • Updated documentation.

2020-02-21 v0.0.1

  • Initial release


Gunnar Grosch - GitHub | Twitter | LinkedIn

Jason Barto - GitHub | Twitter | LinkedIn


npm i failure-azurefunctions

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