Hello everyone! Today I want to share something that saved me a lot of time – dynamic resource creation in ARM templates.<\/p>
Before, I had a problem. Every time I deployed my template, Azure said “name already exists”. I had to manually change names in my template every time. This was annoying!<\/p>
Then I learned about ARM template functions like uniqueString() and concat(). Now Azure creates unique names automatically. Let me show you!<\/p>
Look at my old Web App template:<\/p>
{\n \"type\": \"Microsoft.Web\/sites\",\n \"name\": \"rezawebapp994848\",\n \"properties\": {\n \"name\": \"rezawebapp994848\"\n }\n}<\/code><\/pre>The problem: rezawebapp994848 is hardcoded!<\/p>
What happened when I deployed again?<\/p>
Error: “The website name ‘rezawebapp994848’ already exists”<\/p>
What happened when my friend tried to use my template?<\/p>
Error: “The website name ‘rezawebapp994848’ already exists”<\/p>
I needed unique names every time!<\/p>
Solution: Use Variables and Functions<\/h3>
Here’s my new template with dynamic names:<\/p>
{\n \"$schema\": \"https:\/\/schema.management.azure.com\/schemas\/2019-04-01\/deploymentTemplate.json#\",\n \"contentVersion\": \"1.0.0.0\",\n \"parameters\": {},\n \"functions\": [],\n \"variables\": {\n \"web-app-name\":\"[concat('webapp',uniqueString(resourceGroup().id))]\"\n },\n \"resources\": [\n {\n \"type\": \"Microsoft.Web\/serverfarms\",\n \"apiVersion\": \"2022-03-01\",\n \"name\": \"plan787878\",\n \"location\": \"[resourceGroup().location]\",\n \"sku\": {\n \"name\":\"F1\",\n \"capacity\":1\n },\n \"properties\":{\n \"name\":\"plan787878\"\n }\n },\n {\n \"type\": \"Microsoft.Web\/sites\",\n \"apiVersion\": \"2022-03-01\",\n \"name\": \"[variables('web-app-name')]\",\n \"location\": \"[resourceGroup().location]\",\n \"properties\":{\n \"name\":\"[variables('web-app-name')]\",\n \"serverFarmId\":\"[resourceId('Microsoft.Web\/serverfarms','plan787878')]\"\n },\n \"dependsOn\":[\n \"[resourceId('Microsoft.Web\/serverfarms','plan787878')]\"\n ]\n }\n ],\n \"outputs\": {}\n}<\/code><\/pre>Now look at the variables section:<\/p>
\"variables\": {\n \"web-app-name\":\"[concat('webapp',uniqueString(resourceGroup().id))]\"\n}<\/code><\/pre>And how I use it in the resource:<\/p>
\"name\": \"[variables('web-app-name')]\"<\/code><\/pre>What does this do? Let me explain!<\/p>
Understanding uniqueString() Function<\/h3>
The uniqueString() function creates a unique hash from input.<\/p>
uniqueString(resourceGroup().id)<\/code><\/pre>This takes the resource group ID and creates a unique string from it.<\/p>
Example:<\/p>
- Resource Group ID: \/subscriptions\/abc123\/resourceGroups\/my-rg<\/li>
- uniqueString result: ghe7d4kj2p5a<\/li><\/ul>
The result is always:<\/p>
- 13 characters long<\/li>
- Only lowercase letters and numbers<\/li>
- Same for same input (deterministic)<\/li>
- Different for different input<\/li><\/ul>
So if I use resource group my-rg, I always get ghe7d4kj2p5a. If you use resource group your-rg, you get different string like k8j3h5m9n2p4.<\/p>
This is perfect! Each person gets their own unique name.<\/p>
Understanding concat() Function<\/h3>
The concat() function joins strings together.<\/p>
concat('webapp', uniqueString(resourceGroup().id))<\/code><\/pre>This joins:<\/p>
- webapp (my prefix)<\/li>
- ghe7d4kj2p5a (unique string)<\/li><\/ul>
Result: webappghe7d4kj2p5a<\/p>
Now every deployment gets unique name automatically!<\/p>
Understanding Variables Section<\/h3>\"variables\": {\n \"web-app-name\":\"[concat('webapp',uniqueString(resourceGroup().id))]\"\n}<\/code><\/pre>Variables are like shortcuts. I define the name once in variables, then use it many times in resources.<\/p>
To use a variable:<\/p>
\"name\": \"[variables('web-app-name')]\"<\/code><\/pre>Why use variables?<\/p>
- Define once, use many times<\/li>
- Easy to change later<\/li>
- Makes template cleaner<\/li>
- No copy-paste errors<\/li><\/ol>
Real Example: Web App with Linked SQL Template<\/h3>
Now I want to make BOTH Web App and SQL Server names unique. Here’s my complete example:<\/p>
Main template:<\/p>
{\n \"$schema\": \"https:\/\/schema.management.azure.com\/schemas\/2019-04-01\/deploymentTemplate.json#\",\n \"contentVersion\": \"1.0.0.0\",\n \"parameters\": {},\n \"functions\": [],\n \"variables\": {\n \"web-app-name\":\"[concat('webapp',uniqueString(resourceGroup().id))]\"\n },\n \"resources\": [\n {\n \"type\": \"Microsoft.Web\/serverfarms\",\n \"apiVersion\": \"2022-03-01\",\n \"name\": \"plan787878\",\n \"location\": \"[resourceGroup().location]\",\n \"sku\": {\n \"name\":\"F1\",\n \"capacity\":1\n },\n \"properties\":{\n \"name\":\"plan787878\"\n }\n },\n {\n \"type\": \"Microsoft.Web\/sites\",\n \"apiVersion\": \"2022-03-01\",\n \"name\": \"[variables('web-app-name')]\",\n \"location\": \"[resourceGroup().location]\",\n \"properties\":{\n \"name\":\"[variables('web-app-name')]\",\n \"serverFarmId\":\"[resourceId('Microsoft.Web\/serverfarms','plan787878')]\"\n },\n \"dependsOn\":[\n \"[resourceId('Microsoft.Web\/serverfarms','plan787878')]\"\n ]\n },\n {\n \"type\":\"Microsoft.Resources\/deployments\",\n \"apiVersion\": \"2021-04-01\",\n \"name\":\"LinkedTemplate\",\n \"properties\": {\n \"mode\": \"Incremental\",\n \"templateLink\": {\n \"uri\": \"https:\/\/templatestore465656.blob.core.windows.net\/templates\/sqldatabase.json\",\n \"contentVersion\":\"1.0.0.0\"\n },\n \"parametersLink\": {\n \"uri\": \"https:\/\/templatestore465656.blob.core.windows.net\/templates\/sqldatabase-parameters.json\",\n \"contentVersion\":\"1.0.0.0\"\n }\n }\n }\n ],\n \"outputs\": {\n \"webappname\": {\n \"type\": \"string\",\n \"value\":\"[variables('web-app-name')]\"\n },\n \"sqlserverfqdn\": {\n \"type\": \"string\",\n \"value\":\"[reference('LinkedTemplate').outputs.sqlserverfqdn.value]\"\n }\n }\n}<\/code><\/pre>SQL template (linked):<\/p>
{\n \"$schema\": \"https:\/\/schema.management.azure.com\/schemas\/2019-04-01\/deploymentTemplate.json#\",\n \"contentVersion\": \"1.0.0.0\",\n \"parameters\": {\n \"SQLLogin\": {\n \"type\":\"string\",\n \"metadata\":{\n \"description\":\"The administrator user name\"\n }\n },\n \"SQLPassword\": {\n \"type\":\"secureString\",\n \"metadata\":{\n \"description\":\"The administrator password\"\n }\n }\n },\n \"functions\": [],\n \"variables\": {\n \"sql-server-name\":\"[concat('server',uniqueString(resourceGroup().id))]\"\n },\n \"resources\": [\n {\n \"type\": \"Microsoft.Sql\/servers\",\n \"apiVersion\": \"2022-02-01-preview\",\n \"name\": \"[variables('sql-server-name')]\",\n \"location\": \"[resourceGroup().location]\",\n \"properties\":{\n \"administratorLogin\": \"[parameters('SQLLogin')]\",\n \"administratorLoginPassword\": \"[parameters('SQLPassword')]\"\n }\n },\n {\n \"type\": \"Microsoft.Sql\/servers\/databases\",\n \"apiVersion\": \"2022-02-01-preview\",\n \"name\": \"[format('{0}\/{1}',variables('sql-server-name'),'appdb')]\",\n \"location\": \"[resourceGroup().location]\",\n \"sku\":{\n \"name\":\"Basic\",\n \"tier\":\"Basic\"\n },\n \"properties\":{},\n \"dependsOn\":[\n \"[resourceId('Microsoft.Sql\/servers',variables('sql-server-name'))]\"\n ]\n }\n ],\n \"outputs\": {\n \"sqlserverfqdn\": {\n \"type\": \"string\",\n \"value\":\"[reference(variables('sql-server-name')).fullyQualifiedDomainName]\"\n }\n }\n}<\/code><\/pre>Now both Web App and SQL Server get unique names automatically!<\/p>
Understanding Outputs<\/h3>
Look at the outputs section in my templates:<\/p>
In main template:<\/p>
\"outputs\": {\n \"webappname\": {\n \"type\": \"string\",\n \"value\":\"[variables('web-app-name')]\"\n },\n \"sqlserverfqdn\": {\n \"type\": \"string\",\n \"value\":\"[reference('LinkedTemplate').outputs.sqlserverfqdn.value]\"\n }\n}<\/code><\/pre>In SQL template:<\/p>
\"outputs\": {\n \"sqlserverfqdn\": {\n \"type\": \"string\",\n \"value\":\"[reference(variables('sql-server-name')).fullyQualifiedDomainName]\"\n }\n}<\/code><\/pre>Outputs let you get information AFTER deployment.<\/p>
After I deploy, Azure CLI shows me:<\/p>
{\n \"outputs\": {\n \"webappname\": {\n \"type\": \"String\",\n \"value\": \"webappghe7d4kj2p5a\"\n },\n \"sqlserverfqdn\": {\n \"type\": \"String\",\n \"value\": \"serverghe7d4kj2p5a.database.windows.net\"\n }\n }\n}<\/code><\/pre>Now I know:<\/p>
- My Web App name: webappghe7d4kj2p5a<\/li>
- My SQL Server: serverghe7d4kj2p5a.database.windows.net<\/li><\/ul>
I can use these in my CI\/CD pipeline!<\/p>
Getting Outputs from Linked Templates<\/h3>
This is the tricky part:<\/p>
\"value\":\"[reference('LinkedTemplate').outputs.sqlserverfqdn.value]\"<\/code><\/pre>Let me break it down:<\/p>
- reference(‘LinkedTemplate’) – Get the linked template deployment<\/li>
- .outputs – Get the outputs section<\/li>
- .sqlserverfqdn – Get the specific output<\/li>
- .value – Get the actual value<\/li><\/ul>
So I can get data from linked template and pass it to main template outputs!<\/p>
Using Outputs in Azure DevOps Pipeline<\/h3>
Here’s how I use ARM template outputs in my Azure DevOps pipeline. This is from my actual pipeline file:<\/p>
# ASP.NET Core (.NET Framework)\n# Build and test ASP.NET Core projects targeting the full .NET Framework.\n\ntrigger:\n- main\n\npool:\n vmImage: 'windows-latest'\n\nresources:\n- repo: self\n\nvariables:\n solution: '**\/*.sln'\n buildPlatform: 'Any CPU'\n buildConfiguration: 'Release'\n\nstages:\n- stage: Build\n displayName: Build stage\n jobs:\n - job: Build\n displayName: Build\n steps:\n - task: NuGetToolInstaller@1\n\n - task: NuGetCommand@2\n inputs:\n restoreSolution: '$(solution)'\n\n - task: DotNetCoreCLI@2\n displayName: Build\n inputs:\n command: build\n projects: '**\/*.csproj'\n arguments: '--configuration $(buildConfiguration)'\n\n - task: DotNetCoreCLI@2\n inputs:\n command: publish\n publishWebProjects: True\n arguments: '--configuration $(BuildConfiguration) --output $(Build.ArtifactStagingDirectory)'\n zipAfterPublish: True\n\n - task: PublishPipelineArtifact@1\n inputs:\n targetPath: '$(Build.ArtifactStagingDirectory)'\n artifactName: 'sqlapp-artifact'\n\n - task: PublishPipelineArtifact@1\n inputs:\n targetPath: '$(Build.SourcesDirectory)\/sqlapp\/Templates'\n artifactName: 'template-artifact'\n\n- stage: Deploy\n displayName: Deployment stage\n jobs:\n - job: Deploy\n displayName: Deploy\n steps:\n\n - download: current\n artifact: sqlapp-artifact\n\n - download: current\n artifact: template-artifact\n\n - pwsh: |\n Get-ChildItem -Path $(Pipeline.Workspace)\\*.* -Recurse -Force | Out-String -Width 180\n errorActionPreference: continue\n displayName: 'List content'\n continueOnError: true<\/code><\/pre> - task: AzureResourceManagerTemplateDeployment@3\n displayName: 'ARM Template deployment: Resource Group scope'\n inputs:\n azureResourceManagerConnection: 'Azure subscription 1 (6912d7a0-bc28-459a-9407-33bbba641c07)'\n subscriptionId: '6912d7a0-bc28-459a-9407-33bbba641c07'\n resourceGroupName: 'template-grp'\n location: 'North Europe'\n csmFile: '$(Pipeline.Workspace)\/template-artifact\/main.json'\n action: 'Create Or Update Resource Group'\n deploymentMode: 'Incremental'\n\n - task: SqlAzureDacpacDeployment@1\n displayName: 'Azure SQL InlineSqlTask'\n inputs:\n azureSubscription: 'Azure subscription 1 (6912d7a0-bc28-459a-9407-33bbba641c07)'\n ServerName: sqlserver8000505.database.windows.net\n DatabaseName: appdb\n SqlUsername: sqlusr\n SqlPassword: 'Azure@123'\n deployType: InlineSqlTask\n SqlInline: |\n IF (NOT EXISTS (SELECT * \n FROM INFORMATION_SCHEMA.TABLES \n WHERE TABLE_SCHEMA = 'dbo' \n AND TABLE_NAME = 'Products'))\n BEGIN\n\n CREATE TABLE Products\n (\n ProductID int,\n ProductName varchar(1000),\n Quantity int\n )\n\n\n INSERT INTO Products(ProductID,ProductName,Quantity) VALUES (1,'Mobile',100)\n\n INSERT INTO Products(ProductID,ProductName,Quantity) VALUES (2,'Laptop',200)\n\n INSERT INTO Products(ProductID,ProductName,Quantity) VALUES (3,'Tabs',300)\n\n END\n IpDetectionMethod: IPAddressRange\n StartIpAddress: 0.0.0.0\n EndIpAddress: 0.0.0.0\n DeleteFirewallRule: false\n\n - task: AzureRmWebAppDeployment@4\n displayName: 'Azure App Service Deploy'\n inputs:\n azureSubscription: 'Azure subscription 1 (6912d7a0-bc28-459a-9407-33bbba641c07)'\n WebAppName: newapp1094848\n Package: '$(Pipeline.Workspace)\/sqlapp-artifact\/**\/*.zip'\n\n - task: AzureAppServiceSettings@1\n displayName: 'Azure App Service Settings: newapp1094848'\n inputs:\n azureSubscription: 'Azure subscription 1 (6912d7a0-bc28-459a-9407-33bbba641c07)'\n appName: newapp1094848\n resourceGroupName: 'template-grp'\n connectionStrings: |\n [\n {\n \"name\": \"SQLConnection\",\n \"value\": \"Server=tcp:sqlserver8000505.database.windows.net,1433;Initial Catalog=appdb;Persist Security Info=False;User ID=sqlusr;Password=Azure@123;MultipleActiveResultSets=False;Encrypt=True;TrustServerCertificate=False;Connection Timeout=30;\",\n \"type\": \"SQLAzure\",\n \"slotSetting\": false\n }\n ]<\/code><\/pre>In my pipeline, I deploy the ARM template in the Deploy stage.<\/p>
The key task is:<\/p>
- task: AzureResourceManagerTemplateDeployment@3\n displayName: 'ARM Template deployment: Resource Group scope'\n inputs:\n azureResourceManagerConnection: 'Azure subscription 1 (6912d7a0-bc28-459a-9407-33bbba641c07)'\n subscriptionId: '6912d7a0-bc28-459a-9407-33bbba641c07'\n resourceGroupName: 'template-grp'\n location: 'North Europe'\n csmFile: '$(Pipeline.Workspace)\/template-artifact\/main.json'\n action: 'Create Or Update Resource Group'\n deploymentMode: 'Incremental'<\/code><\/pre>This task:<\/p>
- Takes my main.json template from artifacts<\/li>
- Deploys it to template-grp resource group<\/li>
- Uses Incremental mode (safe!)<\/li>
- Creates Web App with unique name<\/li>
- Calls linked template for SQL Database<\/li><\/ol>
After ARM deployment finishes, I run SQL script to create tables, then deploy my application code to the Web App.<\/p>
The pipeline works end-to-end:<\/p>
- Build stage – Build .NET application<\/li>
- Publish artifacts – Application code + ARM templates<\/li>
- Deploy stage – Deploy ARM templates<\/li>
- Create SQL tables with inline SQL script<\/li>
- Deploy application to Web App<\/li>
- Configure connection string<\/li><\/ol>
More Useful Functions<\/h3>
Let me show you other functions I use:<\/p>
Using toLower():<\/p>
\"variables\": {\n \"storage-name\":\"[toLower(concat('storage',uniqueString(resourceGroup().id)))]\"\n}<\/code><\/pre>This makes everything lowercase. Storage account names must be lowercase!<\/p>
Using resourceGroup().location:<\/p>
\"location\": \"[resourceGroup().location]\"<\/code><\/pre>This uses the resource group location automatically. I don’t need to type “North Europe” everywhere!<\/p>
Using multiple concat():<\/p>
\"variables\": {\n \"vm-name\":\"[concat('vm-', parameters('environment'), '-', uniqueString(resourceGroup().id))]\"\n}<\/code><\/pre>If environment parameter is “dev”, result: vm-dev-ghe7d4kj2p5a<\/p>
If environment parameter is “prod”, result: vm-prod-ghe7d4kj2p5a<\/p>
My Mistakes and Fixes<\/h3>
I forgot square brackets around function:<\/p>
\"name\": \"concat('webapp', uniqueString(resourceGroup().id))\"<\/code><\/pre>This doesn’t work! ARM treats it as plain text, not a function.<\/p>
Fix: Add square brackets:<\/p>
\"name\": \"[concat('webapp', uniqueString(resourceGroup().id))]\"<\/code><\/pre>I used wrong variable name:<\/p>
\"variables\": {\n \"webappname\": \"...\"\n}\n\n\/\/ Later in resource\n\"name\": \"[variables('web-app-name')]\" \/\/ Different name!<\/code><\/pre>Error: “The template variable ‘web-app-name’ is not found”<\/p>
Fix: Use exact same name everywhere.<\/p>
I forgot single quotes in concat:<\/p>
concat(webapp, uniqueString(resourceGroup().id)) \/\/ Wrong! Missing quotes<\/code><\/pre>Fix: Add quotes around string:<\/p>
concat('webapp', uniqueString(resourceGroup().id)) \/\/ Correct!<\/code><\/pre>I tried to use outputs before deployment finished:<\/p>
In same template, I tried:<\/p>
\"resources\": [\n {\n \"name\": \"webapp\",\n \"type\": \"Microsoft.Web\/sites\",\n ...\n },\n {\n \"name\": \"another-resource\",\n \"properties\": {\n \"value\": \"[reference('webapp').outputs.something]\" \/\/ Wrong!\n }\n }\n]<\/code><\/pre>This doesn’t work! I can only use outputs AFTER deployment, not during deployment.<\/p>
Fix: Use dependsOn and reference() correctly, or use outputs only in pipeline steps after deployment.<\/p>
What I Learned<\/h3>- uniqueString() creates unique names – No more “name already exists” errors<\/li>
- concat() joins strings – Easy to add prefixes<\/li>
- Variables make code cleaner – Define once, use many times<\/li>
- Outputs give information – Use in CI\/CD pipelines<\/li>
- Square brackets are required – For all ARM functions<\/li>
- Linked templates can return outputs – Get data from child templates<\/li>
- Azure DevOps can use ARM outputs – Connect templates to pipelines<\/li><\/ol>
Why This Matters<\/h3>
Before dynamic names:<\/p>
- Manual work every deployment<\/li>
- Name conflicts<\/li>
- Hard to share templates<\/li>
- Cannot automate<\/li><\/ul>
After dynamic names:<\/p>
- Deploy unlimited times<\/li>
- No conflicts<\/li>
- Easy to share<\/li>
- Full automation<\/li><\/ul>","protected":false},"excerpt":{"rendered":"
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