ARM Incremental deployment mode - yaml

Question

Consider I have an Azure Function App with some app settings and some functions created via the following YAML task:
- task: AzureResourceManagerTemplateDeployment#3
displayName: 'deploy resources'
inputs:
azureResourceManagerConnection: azureResourceManagerConnection
subscriptionId:subscriptionId
resourceGroupName: rg
location:location
csmFile: template.bicep
csmParametersFile:parameters.json
deploymentMode: 'Incremental'
Let’s say I modified app settings.
If I run the above YAML task in Incremental deployment mode, does that recreate the Azure Function App with the modified app settings and functions or does it just update the app settings - Function app and existing functions stay the same?
Here is how my template.bicep looks like:
var appSettings = [
{
name: 'WEBSITE_ADD_SITENAME_BINDINGS_IN_APPHOST_CONFIG'
value: 1
}
{
name: 'WEBSITE_ENABLE_SYNC_UPDATE_SITE'
value: 1
}
{
name: 'SCM_TOUCH_WEBCONFIG_AFTER_DEPLOYMENT'
value: 0
}
{
name: 'APPINSIGHTS_INSTRUMENTATIONKEY'
value: reference(resourceId(appInsightsResourceGroup, 'microsoft.insights/components/', appInsightsName), '2015-05-01').InstrumentationKey
}
{
name: 'AzureWebJobsStorage'
value: 'DefaultEndpointsProtocol=https;AccountName=${storageAccountName};AccountKey=${listKeys(resourceId(storageAccountResourceGroup, 'Microsoft.Storage/storageAccounts', storageAccountName), providers('Microsoft.Storage', 'storageAccounts').apiVersions[0]).keys[0].value}'
}
{
name: 'WEBSITE_CONTENTAZUREFILECONNECTIONSTRING'
value: 'DefaultEndpointsProtocol=https;AccountName=${storageAccountName};AccountKey=${listKeys(resourceId(storageAccountResourceGroup, 'Microsoft.Storage/storageAccounts', storageAccountName), providers('Microsoft.Storage', 'storageAccounts').apiVersions[0]).keys[0].value}'
}
{
name: 'FUNCTIONS_WORKER_RUNTIME'
value: 'dotnet'
}
{
name: 'FUNCTIONS_EXTENSION_VERSION'
value: '~4'
}
{
name: 'WEBSITE_MAX_DYNAMIC_APPLICATION_SCALE_OUT'
value: maximumElasticWorkerCount
}
{
name: 'appConfigurationEndpoint'
value: appConfigurationEndpoint
}
{
name: 'membershipStorageAccountName'
value: '#Microsoft.KeyVault(SecretUri=${reference(membershipStorageAccountName, '2019-09-01').secretUriWithVersion})'
}
{
name: 'membershipContainerName'
value: '#Microsoft.KeyVault(SecretUri=${reference(membershipContainerName, '2019-09-01').secretUriWithVersion})'
}
]
var stagingSettings = [
{
name: 'WEBSITE_CONTENTSHARE'
value: toLower('functionApp-staging')
}
{
name: 'AzureFunctionsJobHost__extensions__durableTask__hubName'
value: '${solutionAbbreviation}compute${environmentAbbreviationStaging}'
}
{
name: 'AzureWebJobs.StarterFunction.Disabled'
value: 1
}
]
var productionSettings = [
{
name: 'WEBSITE_CONTENTSHARE'
value: toLower('functionApp')
}
{
name: 'AzureFunctionsJobHost__extensions__durableTask__hubName'
value: '${solutionAbbreviation}compute${environmentAbbreviation}'
}
{
name: 'AzureWebJobs.StarterFunction.Disabled'
value: 0
}
]
module functionAppTemplate 'functionApp.bicep' = {
name: 'functionAppTemplater'
params: {
name: '${functionAppName}'
kind: functionAppKind
location: location
servicePlanName: servicePlanName
dataKeyVaultName: dataKeyVaultName
dataKeyVaultResourceGroup: dataKeyVaultResourceGroup
secretSettings: union(appSettings, productionSettings)
}
dependsOn: [
servicePlanTemplate
]
}
module functionAppSlotTemplate 'functionAppSlot.bicep' = {
name: 'functionAppSlotTemplate'
params: {
name: '${functionAppName}/staging'
kind: functionAppKind
location: location
servicePlanName: servicePlanName
dataKeyVaultName: dataKeyVaultName
dataKeyVaultResourceGroup: dataKeyVaultResourceGroup
secretSettings: union(appSettings, stagingSettings)
}
dependsOn: [
functionAppTemplate
]
}
functionapp.bicep
resource functionApp 'Microsoft.Web/sites#2018-02-01' = {
name: name
location: location
kind: kind
properties: {
serverFarmId: resourceId('Microsoft.Web/serverfarms', servicePlanName)
clientAffinityEnabled: false
httpsOnly: true
siteConfig: {
use32BitWorkerProcess : false
appSettings: secretSettings
}
}
identity: {
type: 'SystemAssigned'
}
}
functionAppSlot.bicep
resource functionAppSlot 'Microsoft.Web/sites/slots#2018-11-01' = {
name: name
kind: kind
location: location
properties: {
clientAffinityEnabled: true
enabled: true
httpsOnly: true
serverFarmId: resourceId('Microsoft.Web/serverfarms', servicePlanName)
siteConfig: {
use32BitWorkerProcess : false
appSettings: secretSettings
}
}
identity: {
type: 'SystemAssigned'
}
}

Answer 1

Your Function App will not be recreated. Only the state or values which does not match the desired state are changed.
This means, if you change a setting e.g. FUNCTIONS_EXTENSION_VERSION in the bicep file, it will be changed in the Function App settings.
https://learn.microsoft.com/en-us/azure/azure-resource-manager/templates/overview
Repeatable results: Repeatedly deploy your infrastructure throughout the development lifecycle and have confidence your resources are deployed in a consistent manner. Templates are idempotent, which means you can deploy the same template many times and get the same resource types in the same state. You can develop one template that represents the desired state, rather than developing lots of separate templates to represent updates.