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Services

To share services that other accounts can reach via request reply, you have to Export a Service. Services are associated with the account performing the replies and are advertised in the exporting accounts' JWT.

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Adding a Public Service Export

To add a service to your account:

nsc add export --name help --subject help --service
[ OK ] added public service export "help"

To review the service export:

nsc describe account
╭──────────────────────────────────────────────────────────────────────────────────────╮
│                                   Account Details                                    │
├───────────────────────────┬──────────────────────────────────────────────────────────┤
│ Name                      │ A                                                        │
│ Account ID                │ ADETPT36WBIBUKM3IBCVM4A5YUSDXFEJPW4M6GGVBYCBW7RRNFTV5NGE │
│ Issuer ID                 │ OAFEEYZSYYVI4FXLRXJTMM32PQEI3RGOWZJT7Y3YFM4HB7ACPE4RTJPG │
│ Issued                    │ 2019-12-04 18:20:42 UTC                                  │
│ Expires                   │                                                          │
├───────────────────────────┼──────────────────────────────────────────────────────────┤
│ Max Connections           │ Unlimited                                                │
│ Max Leaf Node Connections │ Unlimited                                                │
│ Max Data                  │ Unlimited                                                │
│ Max Exports               │ Unlimited                                                │
│ Max Imports               │ Unlimited                                                │
│ Max Msg Payload           │ Unlimited                                                │
│ Max Subscriptions         │ Unlimited                                                │
│ Exports Allows Wildcards  │ True                                                     │
├───────────────────────────┼──────────────────────────────────────────────────────────┤
│ Imports                   │ None                                                     │
╰───────────────────────────┴──────────────────────────────────────────────────────────╯

╭────────────────────────────────────────────────────────────╮
│                          Exports                           │
├──────┬─────────┬─────────┬────────┬─────────────┬──────────┤
│ Name │ Type    │ Subject │ Public │ Revocations │ Tracking │
├──────┼─────────┼─────────┼────────┼─────────────┼──────────┤
│ help │ Service │ help    │ Yes    │ 0           │ -        │
╰──────┴─────────┴─────────┴────────┴─────────────┴──────────╯

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Importing a Service

Importing a service enables you to send requests to the remote Account. To import a Service, you have to create an Import. To create an import you need to know:

  • The exporting account’s public key

  • The subject the service is listening on

  • You can map the service’s subject to a different subject

  • Self-imports are not valid; you can only import services from other accounts.

To learn how to inspect a JWT from an account server, check this articlearrow-up-right.

First let's create a second account to import the service into:

Add the import of the subject 'help'

Verifying our work:

Let's also add a user to make requests from the service:

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Pushing the changes to the nats servers

If your nats servers are configured to use the built-in NATS resolver, remember that you need to 'push' any account changes you may have done (locally) using nsc add to the servers for those changes to take effect.

e.g. nsc push -i or nsc push -a B -u nats://localhost

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Testing the Service

To test the service, we can install the 'nats' CLI tool:

Set up a process to handle the request. This process will run from account 'A' using user 'U':

Remember you can also do:

Send the request:

The service receives the request:

And the response is received by the requestor:

Or more simply:

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Securing Services

If you want to create a service that is only accessible to accounts you designate you can create a private service. The export will be visible in your account, but subscribing accounts will require an authorization token that must be created by you and generated specifically for the requesting account. The authorization token is simply a JWT signed by your account where you authorize the client account to import your service.

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Creating a Private Service Export

As before, we declared an export, but this time we added the --private flag. The other thing to note is that the subject for the request has a wildcard. This enables the account to map specific subjects to specifically authorized accounts.

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Generating an Activation Token

For the foreign account to import a private service and be able to send requests, you have to generate an activation token. The activation token in addition to granting permission to the account allows you to subset the service’s subject:

To generate a token, you’ll need to know the public key of the account importing the service. We can easily find the public key for account B by running:

The command took the account that has the export ('A'), the public key of account B, the subject where requests from account B will be handled, and an output file where the token can be stored. The subject for the export allows the service to handle all requests coming in on private.help.*, but account B can only request from a specific subject.

For completeness, the contents of the JWT file looks like this:

When decoded it looks like this:

The token can be shared directly with the client account.

If you manage many tokens for many accounts, you may want to host activation tokens on a web server and share the URL with the account. The benefit to the hosted approach is that any updates to the token would be available to the importing account whenever their account is updated, provided the URL you host them in is stable. When using a JWT account server, the tokens can be stored right on the server and shared by an URL that is printed when the token is generated.

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Importing a Private Service

Importing a private service is more natural than a public one because the activation token stores all the necessary details. Again, the token can be an actual file path or a remote URL.

Describe account B

When importing a service, you can specify the local subject you want to use to make requests. The local subject in this case is private.help. However when the request is forwarded by NATS, the request is sent on the remote subject.

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Testing the Private Service

Testing a private service is no different than a public one:

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