sbt "Coursier" Resolution Fails in CI

sbt’s Coursier resolver could not assemble the dependency graph. Either an artifact genuinely is not on the configured resolvers, a resolver is missing, or a repository returned a transient error.

What this error means

sbt update/compile fails with a Coursier "not found" or resolution error naming a module and the repositories it searched. A missing-artifact case fails every time; a transient repo error passes on retry.

sbt output

[error] Error downloading com.example:widgets_2.13:1.4.0
[error]   not found: https://repo1.maven.org/maven2/com/example/widgets_2.13/1.4.0/...
[error]   not found: /root/.ivy2/local/com.example/widgets_2.13/1.4.0/...

Common causes

Artifact not on the configured resolvers

The module lives on a repository not declared in resolvers, or the version/cross-version does not exist, so Coursier finds it nowhere.

Transient repository error

A 5xx or reset from Maven Central / a mirror interrupts resolution. These clear on retry and are unrelated to your build definition.

How to fix it

Declare the resolver and verify the coordinates

Add the repository hosting the artifact and confirm the version/cross-version exists.

build.sbt

// build.sbt
resolvers += "Internal" at "https://your-org.example.com/maven"
libraryDependencies += "com.example" %% "widgets" % "1.4.0"

Retry and cache for transient errors

Terminal

for i in 1 2 3; do sbt update && break || sleep 15; done
# cache ~/.cache/coursier and ~/.ivy2/cache between runs

How to prevent it

Declare every resolver your dependencies need.
Cache ~/.cache/coursier and ~/.ivy2/cache keyed on build files.
Use %% and pin scalaVersion so cross-version artifacts resolve.