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ELEMENT 31

Glossary: stable address

A stable address is the fixed place a customer's applications call to reach an agent on Czar. The address stays put; the operator chooses which version answers.

· 2 min read

IN SHORT

A stable address is the fixed place on the Czar appliance that a customer's own applications call to send a packet to an agent. Deploying points the address at one published version. The address does not change when a new version is published; the operator points it at the new version, points it back if the version is wrong, or turns it off.

A stable address is the fixed endpoint on the Czar appliance that the customer's own applications call to hand a packet to an agent, and that the operator points at exactly one published version at a time.

Why it matters

The desk's applications should not have to change every time the agent does. With a stable address, the system behind the front door calls the same place whether the agent is on its first version or its tenth. Publishing and rollback happen on the appliance side, invisible to the caller.

The address is also the operator's control over whether the agent is live at all. Turning it off stops new runs without discarding any version. That gives a site a plain, reversible way to pause an agent while a question is answered, without touching the applications that call it or the versions on the appliance.

How it works here

When an operator publishes a version, nothing is live yet. Deploying points the agent's stable address at that version. From then on, a packet arriving at the address starts a run of that version, on the appliance, within that version's bounds. One live version at a time: the address never points at two.

When the operator publishes a new version, they point the address at it. If the new version is wrong, they point the address back at an earlier published version. Each pointing is written down with the operator's name and the version chosen, so the record shows which version was live at any moment. The operator can also turn the address on or off, and that too is recorded.

  • Version: what the address points at.
  • Agency Studio: where the design behind a version is made.
  • Run record: what each packet arriving at the address leaves behind.

Questions this raises

Does the address change when a new version is published?
No. The address stays the same and the operator points it at the new version. The applications that call it keep calling the same place and get the new behavior without any change on their side.
What happens to a packet sent to an address that is turned off?
No run starts. The operator turning the address off is how a site stops an agent without unpublishing anything, and turning it back on resumes with whichever version it points at.
Can one version be behind more than one address?
The same design can be published and pointed at on more than one appliance in an estate, each with its own address. Within one appliance, each agent has its own address pointing at its own live version.

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