setDefaultDynamicBackendConfig()

The setDefaultDynamicBackendConfig() allows setting backend configuration defaults that should apply to any newly created dynamic backends via the new Backend() constructor.

Parameters

• defaultDynamicBackendConfig

  • : An Object which contains the generic configuration options to apply to newly created Backends.
    • connectTimeout : number optional
      • Maximum duration in milliseconds to wait for a connection to this backend to be established.
      • If exceeded, the connection is aborted and a 503 response will be presented instead.
      • Throws a RangeError if the value is negative or greater than or equal to 2^32
    • firstByteTimeout : number optional
      • Maximum duration in milliseconds to wait for the server response to begin after a TCP connection is established and the request has been sent.
      • If exceeded, the connection is aborted and a 503 response will be presented instead.
      • Throws a RangeError if the value is negative or greater than or equal to 2^32
    • betweenBytesTimeout : number optional
      • Maximum duration in milliseconds that Fastly will wait while receiving no data on a download from a backend.
      • If exceeded, the response received so far will be considered complete and the fetch will end.
      • Throws a RangeError if the value is negative or greater than or equal to 2^32
    • useSSL : boolean optional
      • Whether or not to require TLS for connections to this backend.
    • dontPool : boolean optional
      • Determine whether or not connections to the same backend should be pooled across different sessions.
      • Fastly considers two backends “the same” if they're registered with the same name and the exact same settings.
      • In those cases, when pooling is enabled, if Session 1 opens a connection to this backend it will be left open, and can be re-used by Session 2.
      • This can help improve backend latency, by removing the need for the initial network / TLS handshake(s).
      • By default, pooling is enabled for dynamic backends.
    • tlsMinVersion : 1 | 1.1 | 1.2 | 1.3 optional
      • Minimum allowed TLS version on SSL connections to this backend.
      • If the backend server is not able to negotiate a connection meeting this constraint, a 503 response will be presented instead.
      • Throws a RangeError if the value is not 1, 1.1, 1.2, or 1.3
    • tlsMaxVersion : 1 | 1.1 | 1.2 | 1.3 optional
      • Maximum allowed TLS version on SSL connections to this backend.
      • If the backend server is not able to negotiate a connection meeting this constraint, a 503 response will be presented instead.
      • Throws a RangeError if the value is not 1, 1.1, 1.2, or 1.3
    • certificateHostname : string optional
      • Define the hostname that the server certificate should declare.
      • Throws a TypeError if the value is an empty string.
    • caCertificate : string optional
      • The CA certificate to use when checking the validity of the backend.
      • Throws a TypeError if the value is an empty string.
    • ciphers : string optional
      • List of OpenSSL ciphers to support for connections to this origin.
      • If the backend server is not able to negotiate a connection meeting this constraint, a 503 response will be presented instead.
      • List of ciphers supported by Fastly.
      • Throws a TypeError if the value is an empty string.
    • clientCertificate : object optional
      • The client certificate to provide for the TLS handshake
      • certificate : string
        • The PEM certificate string.
      • key : SecretStoreEntry
        • The SecretStoreEntry to use for the key, created via SecretStore.prototype.get or alteratively via SecretStore.fromBytes.
    • httpKeepalive : number optional
      • Enable HTTP keepalive, setting the timout in milliseconds.
    • tcpKeepalive : boolean | object optional
      • Enable TCP keepalive. When an object, optionally setting the keepalive configuration options.
      • timeSecs : number optional
        • Configure how long to wait after the last sent data over the TCP connection before starting to send TCP keepalive probes.
      • intervalSecs : number optional
        • Configure how long to wait between each TCP keepalive probe sent to the backend to determine if it is still active.
      • probes : number optional
        • Number of probes to send to the backend before it is considered dead.

Syntax

setDefaultDynamicBackendConfig(defaultConfig);

Return value

None.

Examples

In this example an explicit Dynamic Backend is created and supplied to the fetch request, with timeouts and TLS options provided from the default backend configuration options.

/// <reference types="@fastly/js-compute" />
import { allowDynamicBackends } from 'fastly:experimental';
import { Backend } from 'fastly:backend';
allowDynamicBackends(true);
setDefaultDynamicBackendConfig({
  connectTimeout: 1000,
  firstByteTimeout: 15_000,
  betweenBytesTimeout: 10_000,
  useSSL: true,
  sslMinVersion: 1.3,
  sslMaxVersion: 1.3,
});
async function app() {
  // For any request, return the fastly homepage -- without defining a backend!
  const backend = new Backend({
    name: 'fastly',
    target: 'fastly.com',
    hostOverride: 'www.fastly.com',
  });
  return fetch('https://www.fastly.com/', {
    backend, // Here we are configuring this request to use the backend from above.
  });
}
addEventListener('fetch', (event) => event.respondWith(app(event)));