Docker "failed to solve: no active session" (BuildKit) in CI

By Kaveh Alemi·Latchkey

buildx opens a session with buildkitd to stream the build context, secrets, SSH, and registry auth. If that session is gone when the solve needs it - a dropped connection, a recycled builder, or a daemon that restarted - BuildKit fails with no active session. It is usually a transient session/connection failure, not a Dockerfile bug.

What this error means

A docker buildx build fails with failed to solve: no active session for <session-id>. A re-run on a fresh builder typically succeeds.

ERROR: failed to solve: no active session for 9f3c2a1b-7d4e-4c2a-a1b2-c3d4e5f60718

Common causes

The buildx session dropped before the solve

A connection blip between buildx and buildkitd loses the session that carries context and secrets.

The builder was recycled mid-build

An ephemeral builder torn down during the job kills the active session.

A stale or misconfigured builder

A buildx builder pointed at a buildkitd that restarted no longer has a live session.

How to fix it

Re-run the build

1. This error is usually transient - retry the job.
2. If it clears on retry, treat it as a session/connection blip.

docker buildx build -t myorg/api:1.4.2 --push .

Recreate and bootstrap the builder

1. Remove the stale builder and create a fresh persistent one.
2. Bootstrap it so a live session is established before the build.

docker buildx rm ci || true
docker buildx create --name ci --driver docker-container --bootstrap --use

How to prevent it

• Use a persistent, bootstrapped builder per job.
• Avoid recycling the builder while a build is in flight.
• Retry transient session failures before deeper debugging.

Frequently asked questions

Related guides

References

• Docker documentation
• Docker build cache
• GitHub Actions documentation