The initial input to the verwalter’s scheduler. It conists of:
- All data in
- All templates and actions in
It’s expected that these files are never mutated. But new ones might be added. E.g. if there is
runtime/v1.0.1/..and new version
runtime/v1.0.2appears verwalter reads it as fast as possible, and makes it available on next scheduler run.
All configuration versions are read by verwalter. So you can write any required logic in scheduler. For example, to arrange a blue/green deployment strategy you may need to keep “blue” configuration around even when no processes running it are present.
- All data in
A data structure that holds information about all the services that must run on the whole cluster. This is the result of running a scheduler code.
In fact it’s just a piece of JSON-like data, which you may use in templates when rendering the configurations. It may contain anything, but usually it’s something along lines of nested dicts:
host-name -> process-name -> number-of-instances.
The Lua code that receives a configuration and a state and generates a schedule. Basically it’s just a (pure) function.
A scheduler may do whatever it needs for the transformation. But, but it’s very important to obey the following rules:
- No external data should be used. Just configuration and state.
- No side effects allowed, like writing to the files or even reading current date/time (we provide date/time as part of state, though)
- It shouldn’t be too slow
- deployment id
The unique identifier of the series of the actions that was run to apply certain config. Deployment id is local for single machine, but may span across roles. Single deployment id is used only once, so they refer to the time range when deployment started and finished. Multiple deployments can’t be run on single machines simultaneously.
Not all roles can be deployed with the single deployment id just the ones which need an update. Each role may execute commands only once during single deployment.
There is no direct correspondence between config hash and deployment id. Single config may be deployed multiple times even on single machine. (each time when verwalter is restarted, each time when config changed and then rolled back again). But single deployment may deploy only single configuration. I.e. configuration can’t change during deployment.
And there is no direct match between application update and deployment id. The (rolling) application id usually involves multiple configuration updates. And each configuration update triggers one deployment on each machine. Also multiple rolling updates of different applications may take place at the same time. And all of them correspond to a single configuration change at any point in time.
A single deployment unit. A role has it’s own configuration independent of others(set of versions of containers, set of config templates).
A role may contain multiple containers. And multiple different setups on different nodes. It’s up to a lua configuration.
Usually single role refers to single “sandbox” in lithos, but this limit is not enforced.
Similarly blue/green deploy (or rolling update) between versions is usually performed for a role. Which means each role has it’s own state of the deployment, and multiple roles can be migrated independently. But this is not enforced either. With careful scripting you can do both: synchronize updates of multiple roles or update different processes in single role using some independent states.