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.
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 callback connection settings on a per-request basis. The override settings allow you to specify:
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 #.
Voice webhooks that are retried are not displayed as separate requests in the Request Inspector section of a call's log page in the Console.
The complete list of overrides supported is detailed below:
Parameter: Connect Timeout (ct)
Valid values:
Min: 100Max: 10000
Default:
5000
Notes:
The timeout in milliseconds Twilio will wait to establish its TCP connection to your web server.
Parameter: Read Timeout (rt)
Valid values:
Min: 100Max: 15000
Default:
15000
Notes:
The amount of time in milliseconds after sending your webhook an HTTP request that Twilio will wait for the initial HTTP response packet. Also applies to the amount of time Twilio will wait between individual packets within your HTTP response.
Parameter: Total time (tt)
Valid values:
Min: 100Max: 15000
Default:
15000
Notes:
The total time allowed for all timeouts including retries. If not set, the maximum limit is enforced.
Parameter: Retry count (rc)
Valid values:
Min: 0Max: 5
Default:
1
Notes:
The number of retry attempts Twilio will make if its connection to your webhook fails. To make sure you capture the behaviors you need, make sure to set the Retry Policy ( rp ) value below accordingly
Parameter: Retry policy (rp)
Valid values:
4xx, 5xx, ct, rt, all
Default:
ct
Notes:
The type of failure to retry on:
4xx — Any 4xx response from your web server5xx — Any 5xx response from your web serverct — TCP connect or TLS handshake failurert — No response received within read timeout from your web server. We will not retry on partial response, e.g., missing HTTP content.all — All of the above.Pass as a list of values, e.g., rp=ct,rt
Parameter: SNI (sni)
Valid values:
y, n
Default:
y
Notes:
If set to y we use SNI (default). If set to n we disable SNI.Note Only applies for secure connections (HTTPS)
Parameter: Edge Location (e)
Valid values:
ashburn, dublin, frankfurt, sao-paulo, singapore, sydney, tokyo, or umatilla ashburn-ix, frankfurt-ix, london-ix, san-jose-ix, or singapore-ix (only used with Twilio Interconnect)
Default:
ashburn
Notes:
The Twilio edge location where webhooks egress. This can be a list, and we rotate through the list as retries occur. The order of precedence for edge location is:
e=.e=.If Static Proxy is enabled for the account, the e parameter is ignored.
The values with the -ix suffix are used for Interconnect edges. To allow webhooks to traverse your interconnect, ensure the following:
Otherwise, the webhook will traverse the public internet.
There will be a new HTTP header (I-Twilio-Idempotency-Token), a unique string, that you can use to distinguish retry attempts.
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 supersede these timers; please review your product documentation to help you determine appropriate settings for your use case.
(1) https://example.com/foo?query=123#ct=1000
Connection timeout (time to wait for a connection to be established) of one second.
(2) https://example.com/foo?query=123#ct=1000&rt=1000
Connection timeout (time to wait for a connection to be established) of one second and a Read timeout (time to wait for data to be returned on a connection) of one second.
(3) https://example.com/foo?query=123#rt=5000&rp=ct,rt
Retry on both connect and read timeout, while also reducing the read timeout to five seconds.
(4) https://example.com/foo?query=123#e=ashburn,umatilla
Retry on failure over different edge locations. The 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 one-second connection timeout. If there is no connection in one second, retry twice, i.e., for a total of three attempts to connect.
Connection overrides are available on all product webhooks except for Twilio Conversations and Twilio Frontline. The overrides may be specified in webhook URLs in both the API resource properties and TwiML attributes.
If you have trouble implementing a connection override, you can reach out to our support team for help.