keep-alive 

(Optional) Boolean that indicates whether the HTTP client should attempt to use persistent connections. The default is true.

keep-alive-timeout 

(Optional) The maximum number of seconds to keep a persistent connection open. The default is 29.

always-use-keep-alive 

(Optional) Boolean that indicates whether the HTTP client can reuse existing persistent connections for all types of requests. The default is false, meaning persistent connections will not be reused for non-GET requests nor for requests with a body.

always-retry-stale-keep-alive 

(Optional) Boolean that indicates whether the HTTP client will retry a request even when the retries parameter is set to 0 (zero), provided that the request failed because the persistent connection it used was found to be stale. The default value is false.

retries 

(Optional) The maximum number of times the HTTP client will retry a request when the request returns an error. The default is 3.

Note that the HTTP client only retries requests that returned retryable errors such as a connection timeout, a stale keep-alive connection, and so on. 

Also note that a special situation regarding the reuse of persisent connections arises when the retries parameter is set to 0 (zero) and the keep-alive parameter is set to true. Because retries is set to zero, the HTTP client does not consider any request as retryable, and so does not reuse existing persistent connections; instead, it establishes new connections. In this situation, setting the always-use-keep-alive parameter to true enables the reuse of existing persistent connections.

protocol 

(Optional) HTTP protocol version string. By default, the HTTP client uses either "HTTP/1.0" or "HTTP/1.1" based on the contents of the HTTP request. Do not use the protocol parameter unless you encounter specific protocol interoperability problems. 

proxy-agent 

(Optional) Value of the Proxy-agent HTTP request header. The default is a string that contains the proxy server product name and version.