The NATS server is rejecting connections and messages due to insufficient permissions, preventing clients from publishing or subscribing to topics.
The most common culprit is a misconfiguration in the NATS server’s authorization rules, often involving incorrect subject wildcards or missing permissions for specific HTTP authentication endpoints.
Cause 1: Incorrectly Defined Authorization Rules
Your nkeys or jwt based authorization configuration might be too restrictive, denying access to subjects that your clients actually need to use. This is especially common with wildcards.
Diagnosis:
Check your NATS server’s authorization configuration file (e.g., nats.conf). Look for the authorization block.
Example nats.conf snippet:
authorization {
type: jwt
// ... other jwt config
users: [
{
// ... user specific config
permissions: {
pub: ["data.>" ] // This might be too restrictive
sub: [">" ]
}
}
]
}
Fix:
Broaden the pub or sub permissions to include the necessary subjects. If clients are publishing to analytics.events.user_signup, and your rule is data.>, this will fail. You might need analytics.events.> or even >.
Example corrected nats.conf snippet:
authorization {
type: jwt
// ... other jwt config
users: [
{
// ... user specific config
permissions: {
pub: ["analytics.events.>" ] // Corrected to allow more specific subjects
sub: [">" ]
}
}
]
}
This works because the NATS server performs a direct string comparison against the subject, and wildcards (* for a single token, > for any number of tokens) are evaluated to match the broadest possible set of subjects.
Cause 2: Expired or Invalid JWTs
If you’re using JWT-based authentication, the JSON Web Tokens assigned to your users might have expired or been revoked.
Diagnosis:
Inspect the JWTs your clients are using. You can use jwt.io to decode them and check the exp (expiration) claim. Also, verify the iss (issuer) and sub (subject) claims match your NATS server’s configuration.
Fix:
Generate new JWTs for your clients. Ensure the issuer (nats://your_nats_server_address:4222 or similar) and expiration times are correctly set. You can use the nats jwt command-line tool for this:
nats jwt issue --account <account_key_or_name> --issuer <issuer_key_or_name> --allow-any-account --exp 24h --allow-pub "data.>" --allow-sub "data.>"
This command generates a new JWT with the specified permissions and expiration. The NATS server validates this JWT upon connection, granting access based on its embedded claims.
Cause 3: Missing Account Claim in JWT
When using NATS Accounts (multi-tenancy), the JWT must explicitly define which accounts the user is allowed to operate within.
Diagnosis:
Decode the user JWT and check for the nats.ca (or nats.att) claim. This claim should contain the public key of the account the user belongs to.
Fix:
Ensure the JWT includes the correct account public key in the nats.ca claim. If you’re generating JWTs with nats jwt, use the --account flag:
nats jwt issue --account <account_public_key> --issuer <issuer_key> --exp 24h --allow-pub "data.>"
The NATS server uses the account claim to determine the security context for the connection, filtering permissions based on the authenticated account.
Cause 4: HTTP Authentication Endpoint Issues
If you’re using auth_url in your nats.conf for external authentication, problems with that endpoint can lead to authorization errors. The NATS server might be unable to reach the endpoint, or the endpoint might be returning incorrect status codes or responses.
Diagnosis:
Check the NATS server logs for errors related to auth_url. You can also use curl to test the auth_url directly from the NATS server’s host:
curl -X POST -H "Authorization: Bearer YOUR_TOKEN_HERE" -d '{"token": "USER_TOKEN_FROM_CLIENT"}' http://your.auth.service/auth
Look for non-2xx status codes or unexpected response bodies.
Fix:
Ensure the auth_url is accessible from the NATS server and that it correctly validates tokens, returning a 200 OK status code with a valid NATS user JSON payload on success.
Example successful response from auth_url:
{
"user": "authenticated_user",
"permissions": {
"pub": ["data.>"],
"sub": ["data.>"]
}
}
This allows the NATS server to delegate authentication and authorization decisions to an external service.
Cause 5: Incorrect NKEY Seed/Public Key Mismatch
If you’re using NKEY authentication, the client might be using an incorrect seed key, or the server might have the wrong public key associated with the user.
Diagnosis:
Verify that the NKEY seed file (.nk file) used by the client is the correct one corresponding to the public key configured on the NATS server. You can extract the public key from a seed file using nkey -p <seed_file_path>.
Fix:
Ensure the client is using the correct NKEY seed file. If the public key is listed in the NATS server configuration (e.g., in nats.conf or a linked JWT), verify that it matches the public key derived from the client’s seed file.
Example nats.conf snippet for NKEY:
authorization {
type: nkey
// ... other nkey config
users: [
{
user: "user1"
// Public key derived from user1's seed file
nkey: "SUAXXXXXX..."
permissions: {
pub: ["data.>"]
sub: ["data.>"]
}
}
]
}
The NATS server uses the public key to verify the signature generated by the client’s private key, establishing a trusted identity.
Cause 6: Client Not Sending Credentials
The client application might be failing to send its authentication credentials (like a JWT or NKEY) during the connection handshake.
Diagnosis: Examine the client application’s connection logic. Ensure it’s correctly providing the authentication details to the NATS client library.
Fix: Update the client application to include the necessary authentication credentials when establishing a connection. For example, with the Go NATS client:
import (
"github.com/nats-io/nats.go"
"log"
)
func main() {
// Load your JWT or NKEY seed
jwt, err := nats.LoadClientJWT("path/to/your/user.jwt")
if err != nil {
log.Fatal(err)
}
// Connect with options
nc, err := nats.Connect("nats://localhost:4222",
nats.UserCredentials("path/to/your/user.creds"), // For NKEY
nats.Name("My Awesome Client"),
nats.Token(jwt), // For JWT
)
if err != nil {
log.Fatal(err)
}
defer nc.Close()
log.Printf("Connected to NATS at %s", nc.ConnectedUrl())
}
The NATS client library handles the secure exchange of these credentials with the server, which then uses them for authorization.
The next error you’ll likely encounter, after fixing authorization, is a timeout error if the NATS server itself is unreachable due to network issues or being down.