feat: add workspace-mount-sub-path-expr config option#871
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DrJosh9000 merged 1 commit intoMay 5, 2026
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When set, applies a `subPathExpr` to every /workspace VolumeMount the
controller creates (workspace setup init container, image check init
containers, agent + checkout system containers, and command containers).
This allows a shared workspace volume — e.g. a hostPath rooted at the
node's /var/lib/buildkite-workspaces — to be sliced into per-pod
subdirectories so concurrent jobs on the same node don't collide on
/workspace/build, /workspace/sockets, etc.
The canonical setup is `workspace-mount-sub-path-expr: $(POD_NAME)`
paired with a downward-API POD_NAME env var on the relevant containers
(via pod-spec-patch or the chart's checkout-params / command-params).
Default ("") preserves the previous behavior.
Tests cover both the configured-value-propagates-everywhere case and
the default-no-subPath case.
Use case: enables a per-node shared-cache pattern for `docker run`
workloads — a single dockerd DaemonSet on each node bind-mounts the
shared workspace hostPath, and per-pod subdirectories prevent
concurrent jobs from clobbering each other's workspace state. Without
this option, per-pod isolation is impossible because the workspace
mount is hardcoded with no SubPath.
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Thanks @csweeney-plaid! The idea is sound, and the code LGTM. ✅
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What it is
When set, applies a
subPathExprto every /workspace VolumeMount the controller creates (workspace setup init container, image check init containers, agent + checkout system containers, and command containers).This allows a shared workspace volume — e.g. a hostPath rooted at the node's /var/lib/buildkite-workspaces — to be sliced into per-pod subdirectories so concurrent jobs on the same node don't collide on /workspace/build, /workspace/sockets, etc.
Why
this enables a per-node shared-cache pattern for
docker runworkloads that Plaid is using — a single dockerd DaemonSet on each node bind-mounts the shared workspace hostPath, and per-pod subdirectories prevent concurrent jobs from clobbering each other's workspace state.Without this option, per-pod isolation is impossible because the workspace mount is hardcoded with no SubPath.
Usage
The canonical setup Plaid is using this in is
workspace-mount-sub-path-expr: $(POD_NAME)paired with a downward-API POD_NAME env var on the relevant containers (via pod-spec-patch or the chart's checkout-params / command-params).Default ("") preserves the previous behavior.
Tests cover both the configured-value-propagates-everywhere case and the default-no-subPath case.