Add framework for managing startup dependencies and shutdown #153
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Adds a "Service interface" that when implemented by embedded component services allows generic management of service startup (incl. waiting on dependencies to become ready), readiness, and cancellation. Adds such a generic service manager that works based on expressing service dependencies as directed acyclic graph. Implements signaling readiness to systemd and cancellation of embedded services after interrupts from the system. Refactors the first two services (etcd, kube-apiserver) to illustrate the pattern, using a GenericService implementation to call the legacy code for bringing up non-ported services. Signed-off-by: Frank A. Zdarsky <fzdarsky@redhat.com>
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The PR starts all the embedded services, but some of them haven't been refactored yet and don't implement cancellation (they just execute forever until MicroShift's process terminates). As a result, the behavior (incl. when receiving interrupts) should still be the same. To get a feeling for the UX after refactoring, comment out L80-91 and L95-110 of pkg/cmd/run.go and run. You may need to wipe |
Signed-off-by: Frank A. Zdarsky <fzdarsky@redhat.com>
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Thanks for the review, @rootfs. You mean for hedging against AddService() being called concurrently?
Note that at least currently, the order of adding services is significant (to enforce the invariant of dependencies being added before dependents), so AddService() shouldn't be called concurrently. Otherwise, we'd have to enable topo sorting. See also the comments in AddService() and Run().
How should we proceed? Add mutex proactively or add note in method description?
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this looks good, please finish it up and also run some benchmark to see if the new way accelerates the startup as well. |
As long as the services other than etcd and kube-apiserver (who have a startup dependency already) haven't been ported, I don't expect to see much diff (other than seeing a few less error messages in the log). |
let's merge this one first and please go ahead with another PR for the rest of the services. |
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/lgtm |
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Adds a "Service interface" that when implemented by embedded component services allows generic management of service startup (incl. waiting on dependencies to become ready), readiness, and cancellation.
Adds such a generic service manager that works based on expressing service dependencies as directed acyclic graph.
Implements signaling readiness to systemd and cancellation of embedded services after interrupts from the system.
Refactors the first two services (etcd, kube-apiserver) to illustrate the pattern, using a GenericService implementation to call the legacy code for bringing up non-ported services.
Signed-off-by: Frank A. Zdarsky fzdarsky@redhat.com
Closes #152