Azure Pipelines using YAML for multiple environments (stages) with different variable values but no YAML duplication

Let's suppose I have 3 environments on Azure: Dev, Test and Prod. I have the same pipeline for building and deploying the resources and the code for each one of the environments except for two differences:

• different trigger branch
• different variable values

What is the correct approach for this scenario? Because at least 3 come to my mind, none of which is perfect:

Option 1: I guess I could create a single pipeline on Azure DevOps (triggered by any of 3 branches) with 3 stages for each environment and for each stage add a condition to run depending on the source branch, like this:

condition: eq(variables['Build.SourceBranch'], 'refs/heads/a-branch-name')

and in each stage reference different variables. But this would introduce code duplication in each stage - when adding or modifying a step I would have to remember to edit 3 stages - not desirable.

Option 2: Create 3 separate YAML files in my repository, each one of them with specified trigger branch and referencing the same variable names, then create 3 different pipeline on Azure DevOps, each one of them with different variable values. But this would also introduce code duplication.

Option 3: Create 1 build-and-deploy.yaml file as a template with the steps defined in it and then create another 3 YAML files referring to that template, each with different trigger branch and with different variable values in each Azure Pipeline, like this:

trigger:
  branches:
    include:
    - a-branch-name

steps:
- template: build-and-deploy.yaml
  parameters:
      parameterName1: $(parameterValue1)
      parameterName2: $(parameterValue2)

This seems to be the best option but I haven't seen it used anywhere in the examples so maybe I'm just unaware of downsides of it, if there are any.

Here's how to do it with a shared pipeline config that gets included into env-specific pipelines.

To support 2 environments (dev and prod) you'd need:

• 1 shared pipeline yaml
• 2 env-specific yamls, one for each env
• 2 pipelines created in Azure DevOps, one for each env; each pipeline referencing corresponding yaml

pipeline-shared.yml:

variables:
  ARTIFACT_NAME: ApiBuild
  NPM_CACHE_FOLDER: $(Pipeline.Workspace)/.npm

stages:
  - stage: Build
    displayName: Build
    pool:
      vmImage: 'ubuntu-latest'
      demands: npm
    jobs:
      ...

  - stage: Release
    displayName: Release
    dependsOn: Build
    pool:
      vmImage: 'ubuntu-latest'
    jobs:
      ...

pipeline-dev.yml:

# Trigger builds on commits to branches
trigger:
  - dev

# Do not trigger builds on PRs
pr: none

extends:
  template: pipeline-shared.yml

pipeline-prod.yml

trigger:
  - master

pr: none

extends:
  template: pipeline-shared.yml