31 lines
2.3 KiB
Markdown
31 lines
2.3 KiB
Markdown
# hub-and-spoke architecture
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The "Hub" runs the web application and talks to the Postgres database, while the "Spoke"s are responsible for creating/managing virtual machines. One instance of the capsul-flask application can run in hub mode and spoke mode at the same time.
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The Hub and the Spoke must be configured to communicate securely with each-other over HTTPS. They both have to be able to dial each-other directly. The URLs / auth tokens they use are configured both in the config file (`HUB_URL`, `SPOKE_HOST_ID`, `SPOKE_HOST_TOKEN` and `HUB_TOKEN`) and in the database (the `id`, `https_url`, and `token` columns in the `hosts` table).
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This diagram was created with https://app.diagrams.net/.
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To edit it, download the <a download href="readme/hub-and-spoke.xml">diagram file</a> and edit it with the https://app.diagrams.net/ web application, or you may run the application from [source](https://github.com/jgraph/drawio) if you wish.
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right now I have 2 types of operations, immediate mode and async.
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both types of operations do assignment synchronously. so if the system cant assign the operation to one or more hosts (spokes),
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or whatever the operation requires, then it will fail.
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some operations tolerate partial failures, like, `capacity_avaliable` will succeed if at least one spoke succeeds.
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for immediate mode requests (like `list`, `capacity_avaliable`, `destroy`), assignment and completion of the operation are the same thing.
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for async ones, they can be assigned without knowing whether or not they succeeded (`create`).
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This diagram was created with https://app.diagrams.net/.
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To edit it, download the <a download href="readme/hub-and-spoke.xml">diagram file</a> and edit it with the https://app.diagrams.net/ web application, or you may run the application from [source](https://github.com/jgraph/drawio) if you wish.
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if you issue a create, and it technically could go to any number of hosts, but only one host responds, it will succeed
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but if you issue a create and somehow 2 hosts both think they own that task, it will fail and throw a big error. cuz it expects exactly 1 to own the create task
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currently its not set up to do any polling. its not really like a queue at all. It's all immediate for the most part
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