In the previous blog post, I discussed adding SSL to webhookd. In this post, I will briefly show how to use this solution to deploy Azure resources.
To run webhookd, I deployed a small Standard_B1s machine (1GB RAM, 1 vCPU) with a system assigned managed identity. After deployment, information about the managed identity is available via the Identity link.
Code running on a machine with a managed identity needs to do something specific to obtain information about the identity like a token. With curl, you would issue the following command:
curl 'http://169.254.169.254/metadata/identity/oauth2/token?api-version=2018-02-01&resource=https%3A%2F%2Fmanagement.azure.com%2F' -H Metadata:true -s
The response would be JSON that contains a field called access_token. You could parse out the access_token and then use the token in a call to the Azure Resource Manager APIs. You would use the token in the autorization header. Full details about acquiring these tokens can be found here. On that page, you will find details about acquiring the token with Go, JavaScript and several other languages.
Because we are using webhookd and shell scripts, the Azure CLI is the ideal way to create Azure resources. The Azure CLI can easily authenticate with the managed identity using a simple command: az login –identity. Here’s a shell script that uses it to create a virtual machine:
#!/bin/bash echo "Authenticating...`az login --identity`"
echo "Creating the resource group...`az group create -n $rg -l westeurope`"
echo "Creating the vm...`az vm create --no-wait --size Standard_B1s --resource-group $rg --name $vmname --image win2016datacenter --admin-username azureuser --admin-password $pw`"
The script expects three parameters: rg, vmname and pw. We can pass these parameters as HTTP query parameters. If the above script would be in the ./scripts/vm folder as create.sh, I could do the following call to webhookd:
curl --user api -XPOST "https://<public_server_dns>/vm/create?vmname=myvm&rg=myrg&pw=Abcdefg$$$$!!!!"
The response to the above call would contain the output from the three az commands. The az login command would output the following:
data: {
data: "environmentName": "AzureCloud",
data: "id": "<id>",
data: "isDefault": true,
data: "name": "<subscription name>",
data: "state": "Enabled",
data: "tenantId": "<tenant_id>",
data: "user": {
data: "assignedIdentityInfo": "MSI",
data: "name": "systemAssignedIdentity",
data: "type": "servicePrincipal"
data: }
Notice the user object, which clearly indicates we are using a system-assigned managed identity. In my case, the managed identity has the contributor role on an Azure subscription used for testing. With that role, the shell script has the required access rights to deploy the virtual machine.
As you can see, it is very easy to use webhookd to deploy Azure resources if the Azure virtual machine that runs webhookd has a managed identity with the required access rights.
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