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Webhooks (HTTP callbacks): Connection Overrides

Twilio uses HTTP callbacks (webhooks) to let your application know when events happen, such as receiving an SMS message or getting an incoming phone call. When the event occurs, Twilio makes an HTTP request (usually a POST or a GET) to the URL you configured for the webhook. Twilio's request will include details of the event such as the incoming phone number or the body of an incoming message.

Twilio’s use of HTTP URLs conforms to the standard syntax of a generic URI/URL.

Connection Overrides

Twilio has implemented URL extensions, that can be added to the standard HTTP webhook URL. These extensions give you the ability to override Twilio's default HTTP callbacks connection settings on a per request basis. The override settings allow you to specify:

  • Longer timeouts to better support intermittent network issues between Twilio and your server/application
  • Shorter timeouts to speed up failover (to fallback URL) in the case of an outage on your server/application
  • HTTP callback connection retries on failures/timeouts
  • The egress Twilio Edge (region) for your HTTP callback
  • The total timeout limit for all of the retries to complete
  • The use of Server Name Indication (SNI) if your server/application requires SNI to ensure a proper TLS handshake for all attempts

Connection overrides will be passed on a per webhook URL basis in the form of "fragments". These fragments will contain key-value pairs; key and value are separated by =, pairs are separated by &. The 1st key-value pair start with #.

The complete list of overrides supported are detailed below:

Parameter

Valid values

Default

Notes

Connect Timeout
(ct)

Min: 100

Max: 10000

5000

The timeout in ms for TCP connect to your webserver

Read Timeout
(rt)

Min: 100

Max: 60000

40000

The amount of time in ms after sending HTTP request to wait for the initial HTTP response packet or time between individual response packets

Total time
(tt)

Min: 100

Max: No maximum

No Max

The total time allowed for all timeouts including retries. If not set, no maximum limit is enforced

Retry count
(rc)

Min: 0

Max: 5

1

The number of retry attempts

Retry policy
(rp)

4xx|5xx|ct|rt|all

(list of values. e.g. rp=ct,rt)

ct

The type of failure to retry on:

- 4xx - any 4xx response from your webserver

- 5xx - any 5xx response from your webserver

- ct - TCP connect or TLS handshake failure

- rt - no response received within read timeout from your webserver. We will not retry on partial response (e.g missing HTTP content).

- all - All of the above

SNI
(sni)

y|n|(unset)

(unset)

If set to y we use SNI for all webhooks to customer (including retry).

If set to n we disable SNI for all requests.

If parameter not set the initial request will use SNI, but the retry will not.

NOTE: only applies for secure connections (HTTPS)

Edge Location
(e)

ashburn | dublin | frankfurt | sao-paulo | singapore | sydney | tokyo | umatilla

ashburn-ix | frankfurt-ix | london-ix | san-jose-ix | singapore-ix
(only used with Twilio Interconnect)

ashburn

(Beta)

The Twilio edge location where webhooks egress. This can be a list and we rotate through the list as retries happen.

Th order of presedence for edge location: (1) Twilio Interconnect Edge if specified in (e=), (2) Static Proxy if enabled, (3) Public Edge if specified in (e=), (4) Default

If staticproxy is enabled for the account the 'e' parameter is ignored.

There will be a new HTTP header (I-Twilio-Idempotency-Token), a unique string, that you can use to distinguish retry attempts.

NOTE: Due to the real-time nature of voice calls, there is a hard upper timeout of 15 seconds imposed by Twilio on all call-related HTTP requests. This hard limit overrides any of the timers described above on call-processing requests, and is present to help to ensure a good end-user calling experience.

There are also other product and resource-related timers which may supercede these timers; please review your product documentation to help you determine appropriate settings for your use-case.

Examples

(1) https://example.com/foo?query=123#ct=1000

Connection timeout (time to wait for a connection to be established) of 1 sec

(2) https://example.com/foo?query=123#ct=1000&rt=1000

Connection timeout (time to wait for a connection to be established) of 1 sec and a Read timeout (time to wait for data to be returned on a connection) of 1 sec

(3) https://example.com/foo?query=123#rt=5000&rp=ct,rt

Retry on both connect and read timeout, while also reducting the read timeout to 5 seconds.

(4) https://example.com/foo?query=123#e=ashburn,umatilla

Retry on failure over different edge location. First attempt goes out over Ashburn, second attempt goes out over Umatilla (Oregon).

(5) https://example.com/foo?query=123#rc=2&ct=1000

Retry on connection failure, but with a 1s connection timeout. If there is no connection in 1 second, retry (twice) - for a total of three attempts to connect.

Where are these Overrides Available?

Overrides may be specified in webhook URLs in both the API resource properties and TwiML attributes.

Here is the complete list of resources and attributes currently supported:

API Resource Properties:

IncomingPhoneNumber properties

(Phone Numbers / Manage Numbers / Active Numbers in Twilio Console)

  • voice_url
  • voice_fallback_url
  • status_callback

SipDomain properties

(Voice / SIP Domains / Domains / in Twilio Console)

  • voice_url
  • voice_fallback_url
  • voice_status_callback_url

TwiML App properties

(Voice / TwiML / TwiML Apps / in Twilio Console)

  • voice_url
  • voice_fallback_url
  • status_callback

Calls resource (Initiating a call using API)

  • url
  • fallbackUrl
  • statusCallback

TwiML attributes:

<Dial> attributes

  • action
  • recordingStatusCallback

<Client> <Number> <Sip> attributes

  • url
  • statusCallback

<Enqueue> attributes

  • waitUrl
  • action

<Queue> attributes

  • url

<Gather> attributes

  • action
  • partialResultCallback

<Pay> attributes

  • action
  • statusCallback

<Record> attributes

  • action
  • recordingStatusCallbackMethod
  • transcribeCallback

<Redirect> attributes

  • Noun
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