Backend
A backend (also sometimes called an origin server) is a server identified by IP address or hostname, from which Fastly will fetch your content. There can be multiple backends attached to a service, but each backend is specific to one service. By default, if only one backend is defined in a service configuration, it will be used for all requests provided it meets the conditions attached to it, if any. If multiple backends are defined, the backend that is used for a request is the one with the highest-priority condition attached to it, out of all conditions that this request satisfies. If multiple conditions match the request with the same (highest) priority, one is chosen arbitrarily. If there are no backends with conditions that match the request, then the backend without any conditions is chosen. If there are multiple such backends, one is chosen arbitrarily. The behavior described above can be modified by using the auto_loadbalance field described below. These endpoints can be used with static backends only, not dynamic backends.
Data model
address | string | A hostname, IPv4, or IPv6 address for the backend. This is the preferred way to specify the location of your backend. | |
auto_loadbalance | boolean | Whether or not this backend should be automatically load balanced. If true, all backends with this setting that don't have a request_condition will be selected based on their weight. | |
between_bytes_timeout | integer | 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. May be set at runtime using bereq.between_bytes_timeout. | |
client_cert | string | Unused. | |
comment | string | A freeform descriptive note. | |
connect_timeout | integer | Maximum duration in milliseconds to wait for a connection to this backend to be established. If exceeded, the connection is aborted and a synthetic 503 response will be presented instead. May be set at runtime using bereq.connect_timeout. | |
first_byte_timeout | integer | 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 synthetic 503 response will be presented instead. May be set at runtime using bereq.first_byte_timeout. | |
healthcheck | string | The name of the healthcheck to use with this backend. | |
hostname | string | The hostname of the backend. May be used as an alternative to address to set the backend location. | |
ipv4 | string | IPv4 address of the backend. May be used as an alternative to address to set the backend location. | |
ipv6 | string | IPv6 address of the backend. May be used as an alternative to address to set the backend location. | |
keepalive_time | integer | How long in seconds to keep a persistent connection to the backend between requests. By default, Varnish keeps connections open as long as it can. | |
max_conn | integer | Maximum number of concurrent connections this backend will accept. | |
max_tls_version | string | Maximum allowed TLS version on SSL connections to this backend. If your backend server is not able to negotiate a connection meeting this constraint, a synthetic 503 error response will be generated. | |
min_tls_version | string | Minimum allowed TLS version on SSL connections to this backend. If your backend server is not able to negotiate a connection meeting this constraint, a synthetic 503 error response will be generated. | |
name | string | The name of the backend. | |
override_host | string | If set, will replace the client-supplied HTTP Host header on connections to this backend. Applied after VCL has been processed, so this setting will take precedence over changing bereq.http.Host in VCL. | |
port | integer | Port on which the backend server is listening for connections from Fastly. Setting port to 80 or 443 will also set use_ssl automatically (to false and true respectively), unless explicitly overridden by setting use_ssl in the same request. | |
request_condition | string | Name of a Condition, which if satisfied, will select this backend during a request. If set, will override any auto_loadbalance setting. By default, the first backend added to a service is selected for all requests. | |
share_key | string | Value that when shared across backends will enable those backends to share the same health check. | |
shield | string | Identifier of the POP to use as a shield. | |
ssl_ca_cert | string | CA certificate attached to origin. | |
ssl_cert_hostname | string | Overrides ssl_hostname, but only for cert verification. Does not affect SNI at all. | |
ssl_check_cert | boolean | Be strict on checking SSL certs. [Default true] | |
ssl_ciphers | string | List of OpenSSL ciphers to support for connections to this origin. If your backend server is not able to negotiate a connection meeting this constraint, a synthetic 503 error response will be generated. | |
ssl_client_cert | string | Client certificate attached to origin. | |
ssl_client_key | string | Client key attached to origin. | |
ssl_hostname | string | Deprecated. Use ssl_cert_hostname and ssl_sni_hostname to configure certificate validation. | |
ssl_sni_hostname | string | Overrides ssl_hostname, but only for SNI in the handshake. Does not affect cert validation at all. | |
tcp_keepalive_enable | boolean | Whether to enable TCP keepalives for backend connections. Varnish defaults to using keepalives if this is unspecified. | |
tcp_keepalive_interval | integer | Interval in seconds between subsequent keepalive probes. | |
tcp_keepalive_probes | integer | Number of unacknowledged probes to send before considering the connection dead. | |
tcp_keepalive_time | integer | Interval in seconds between the last data packet sent and the first keepalive probe. | |
use_ssl | boolean | Whether or not to require TLS for connections to this backend. | |
weight | integer | Weight used to load balance this backend against others. May be any positive integer. If auto_loadbalance is true, the chance of this backend being selected is equal to its own weight over the sum of all weights for backends that have auto_loadbalance set to true. | |
created_at | string | Date and time in ISO 8601 format. Read-only. | |
deleted_at | string | Date and time in ISO 8601 format. Read-only. | |
locked | boolean | Indicates whether the version of the service this backend is attached to accepts edits. Read-only. | |
service_id | string | Alphanumeric string identifying the service. Read-only. | |
updated_at | string | Date and time in ISO 8601 format. Read-only. | |
version | integer | Integer identifying a service version. Read-only. |
