By default when you build your project in Azure DevOps pipelines, any package dependencies will be restored as part of the build process. Of course if you have a large list of packages, this can take a long time. Let’s see how we can reduce build time by using Nuget package caching
Lock dependencies using package.lock.json
Before we can use the cache task, we need to lock our project’s dependencies. This is done through a package.lock.json file that will be used to generate a unique key for our cache.
We don’t have to create this package.lock.json file ourselves but we can tell msbuild to generate it when building our project by setting the RestorePackagesWithLockFile property to true:
Don’t forget to check your packages.lock.json file into your source code.
Update our Azure DevOps Pipeline
Now we need to update our Azure DevOps pipeline to use the Cache task. This task will use the content of the packages.lock.json to produce a dynamic cache key. This will ensure that every time the file is modified, a new cache key will be generated.
The cache task will set the CACHE_RESTORED variable to true when we have a cache hit. Now we can use this variable in our NuGet restore task to only run this when the CACHE_RESTORED variable is false:
What about Azure DevOps Server?
Important to know is that this feature only works on Azure DevOps in the cloud and not on the on-premise version. Although it is possible to add the Cache task to your pipeline, you will get an error once you try to invoke the pipeline:
Information, Getting a pipeline cache artifact with the following fingerprint: `nuget|"Windows_NT"|YSCGwKQO4VRcWyDWNaFykEpIXXbRcTAlRukqsPhvvaA=`.
##[error]API resource location a7c78d38-31a8-417e-ba6b-7e58b352f304 is not registered on https://servername/tfs/DefaultCollection/.
Finishing: Cache