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TLS Configuration

The NATS server uses modern TLS semantics to encrypt client, route, and monitoring connections. Server configuration revolves around a tls map, which has the following properties:

Property Description
ca_file TLS certificate authority file.
cert_file TLS certificate file.
cipher_suites When set, only the specified TLS cipher suites will be allowed. Values must match the golang version used to build the server.
curve_preferences List of TLS cipher curves to use in order.
insecure Skip certificate verification.
key_file TLS certificate key file.
timeout TLS handshake timeout in fractional seconds. Default set to 2 seconds.
verify_and_map If true, require and verify client certificates and map certificate values for authentication purposes.
verify If true, require and verify client certificates.

The simplest configuration:

tls: {
  cert_file: "./server-cert.pem"
  key_file: "./server-key.pem"

Or by using server options:

> nats-server --tls --tlscert=./server-cert.pem --tlskey=./server-key.pem
[21417] 2019/05/16 11:21:19.801539 [INF] Starting nats-server version 2.0.0
[21417] 2019/05/16 11:21:19.801621 [INF] Git commit [not set]
[21417] 2019/05/16 11:21:19.801777 [INF] Listening for client connections on
[21417] 2019/05/16 11:21:19.801782 [INF] TLS required for client connections
[21417] 2019/05/16 11:21:19.801785 [INF] Server id is ND6ZZDQQDGKYQGDD6QN2Y26YEGLTH6BMMOJZ2XJB2VASPVII3XD6RFOQ
[21417] 2019/05/16 11:21:19.801787 [INF] Server is ready

Notice that the log indicates that the client connections will be required to use TLS. If you run the server in Debug mode with -D or -DV, the logs will show the cipher suite selection for each connected client:

[22242] 2019/05/16 11:22:20.216322 [DBG] - cid:1 - Client connection created
[22242] 2019/05/16 11:22:20.216539 [DBG] - cid:1 - Starting TLS client connection handshake
[22242] 2019/05/16 11:22:20.367275 [DBG] - cid:1 - TLS handshake complete
[22242] 2019/05/16 11:22:20.367291 [DBG] - cid:1 - TLS version 1.2, cipher suite TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256

When a tls section is specified at the root of the configuration, it also affects the monitoring port if https_port option is specified. Other sections such as cluster can specify a tls block.

TLS Timeout

The timeout setting enables you to control the amount of time that a client is allowed to upgrade its connection to tls. If your clients are experiencing disconnects during TLS handshake, you'll want to increase the value, however, if you do be aware that an extended timeout exposes your server to attacks where a client doesn't upgrade to TLS and thus consumes resources. Conversely, if you reduce the TLS timeout too much, you are likely to experience handshake errors.

tls: {
  cert_file: "./server-cert.pem"
  key_file: "./server-key.pem"
  # clients will fail to connect (value is too low)
  timeout: 0.0001

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