What is auto-creating new Build pipeline? - azure

Question

For a given project, I have four build pipelines, each pipeline Trigger has CI enabled, each has a branch filter for a single branch - master, Staging, QA, development. These work successfully, any completed pull request to one of those four branches are successfully kicking off a build process.
This morning, I created a new branch based off "development" branch. IT was a one-liner change, so I decided to make the change online in the browser using DevOps editor. I saved the change.
Immediately after saving the change online, I saw a new build pipeline was created (I had received an email saying my build failed). What caused the new Build pipeline to be created?
The new build pipeline looks to be auto-created, it is pure YAML:
pool:
vmImage: 'Ubuntu 16.04'
variables:
buildConfiguration: 'Release'
BuildPlatform: 'Any CPU'
Parameters.solution: = '*.sln'
Parameters.ArtifactName: = 'xxxxxx'
steps:
- task: NuGetToolInstaller#0
displayName: 'Use NuGet 4.4.1'
inputs:
versionSpec: 4.4.1
- task: NuGetCommand#2
displayName: 'NuGet restore'
inputs:
restoreSolution: '$(Parameters.solution)'
- task: VSBuild#1
displayName: 'Build solution'
inputs:
solution: '$(Parameters.solution)'
platform: '$(BuildPlatform)'
configuration: '$(BuildConfiguration)'
- task: PublishSymbols#2
displayName: 'Publish symbols path'
inputs:
SearchPattern: '**\bin\**\*.pdb'
PublishSymbols: false
continueOnError: true
- task: PublishBuildArtifacts#1
displayName: 'Publish Artifact'
inputs:
PathtoPublish: '$(build.artifactstagingdirectory)'
ArtifactName: '$(Parameters.ArtifactName)'
In the project, there were no pull requests created, and my private branch, I can see my change.
The email I received had this in the title (actual names removed):
[Build failed] MyProjectName CI - MyProjectName:MyBranchName - MyProejctName - bf9524f9
========
EDIT
I just found there is an azure-pipelines.yml file in the root folder of the branch. the contents match the above. Is this competing with the designer pipelines?

Answer 1

Yaml pipelines are better at scale, you can manage them in a central place, you can easily make mass edits and\or you can make them depend on each other to have more control. Visual designer is only good when you have couple of pipelines or you are only getting started with the whole pipelines thing.
Yaml pipelines do not necessary have to be in azure-pipelines.yml file. I store them in a separate repo :)

Answer 2

Updated comment:
Also the fact that there are no triggers added in your yaml mean that every new branch will queue builds. Read about 'trigger' on the yaml schema to get more understanding on this.
You can use something like below;
trigger:
branches:
include:
- master
- develop
exclude:
- no-build-branch
Given that there is none defined is behaves as below;
trigger:
branches:
include:
- '*'
These two are the same....
Designer picks the azure-pipelines.yml when you click edit. This is the default file name that gets picked up automatically to create a pipeline.
E.g. if you add the pipeline source to azure-pipelines.yml and commit/push it will automatically create a pipeline named 'Repo_Name CI' and queue a build as well.
Any new changes will work on it's merits as per the yaml definition.
you can always use different names and add as many pipelines you want as well.....