Add dualwritehack worker that handles model concerns that need dual writing. #17347
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hpidcock
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/build |
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I completely understand why we need this, but I want to iterate to everyone following along; this will make everything eventually consistent and by eventually consistent, I mean between calls to the model config. This introduces the similar problems we had when we had the model cache and all the horrid distributed problems that it came with. As pointed out, this could help migrate complex refactorings between dqlite and mongo, with dqlite being the source of truth.
There is one ray of light to this as a concept; we will really see if there are any problems to the changestream. This will definitely exercise the underlying eventsource watchers.
| if w.config.StatePool == nil { | ||
| w.config.Logger.Infof("no state pool, doing nothing") | ||
| <-w.catacomb.Dying() | ||
| return w.catacomb.ErrDying() | ||
| } |
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| // ModelConfigDualWrite is a worker that watches dqlite model config and smashes it into | ||
| // mongo state model config. | ||
| func (w *DualWriteWorker) ModelConfigDualWrite(stopCh <-chan struct{}) error { |
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OT: I really wish the simple worker passed in a context that was scoped to the tomb. I'll propose a PR to fix this.
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There are places where we're not writing all the config to dqlite. Considering fan-config is only written to mongo currently, so we need to fix that before this can land. |
hpidcock
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This is a hack. A horrible hack. But it allows us to isolate dual writing concerns to a single model worker that has access to both the model servicefactory and state. That can be deleted when the time comes that we have no mongo.
This is an eventually consistent approach to dual writing.
First example is dual writing model config. It watches model config, and smashes the values into state. Simple.
QA steps
juju.worker.dualwritehack updated model config in mongois in the logs.Documentation changes
Need to add this to the risk registry.
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Jira card: JUJU-