Find Subnet ID for a Canister

Developers
1

In JavaScript, how can I discover which subnet a canister is running on? Or in other words, where can I find the subnet ID for a given canister ID?

2

This is the one part of the registry I know: You can use get_subnet_for_canister. It returns the subnet that canister id is assigned to if the id is assigned to any subnet. It doesn’t check if the canister actually exists

2 Likes
4

HAHAHA, I didn’t pay attention to the thread and thought you were providing an additional answer to the one about “subnet metadata” we discussed yesterday, @Severin. So, I kept going with a solution using Agent-js—without the registry. That’s why I originally replied, mentioning the documentation. :rofl:

Anyway, here’s what I ultimately found, and it seems to work (at least locally). Another trick seems to be using AgentJS’s request and providing a paths equals to subnet.

import {
	CanisterStatus as AgentCanisterStatus,
	AnonymousIdentity,
	type Identity
} from '@dfinity/agent';

export const subnetId = async ({
	canisterId
}: {
	canisterId: string;
}): Promise<string | undefined> => {
	const agent = await getAgent({ identity: new AnonymousIdentity() });

	const path = 'subnet' as const;

	const result = await AgentCanisterStatus.request({
		canisterId: Principal.from(canisterId),
		agent,
		paths: [path]
	});

	const subnet: AgentCanisterStatus.Status | undefined = result.get(path);

	const isSubnetStatus = (
		subnet: AgentCanisterStatus.Status | undefined
	): subnet is AgentCanisterStatus.SubnetStatus =>
		nonNullish(subnet) && typeof subnet === 'object' && 'subnetId' in subnet;

	return isSubnetStatus(subnet) ? subnet.subnetId : undefined;
};

I’ll use it in Juno.

1 Like