1. Concepts Guide
  2. Load Balancing Overview
  3. Session Persistence

Session Persistence

Session persistence is a method to direct all requests originating from a single logical client to a single backend web server. Backend servers that use caching to improve performance, or to enable log-in sessions or shopping carts, can benefit from session persistence.

You enable session persistence when you create a load balancer or when you create a backend set. You can also edit an existing backend set to enable, disable, or change the session persistence configuration.

The Load Balancing service offers two mutually exclusive cookie-based configurations for enabling session persistence: application cookie stickiness and load balancer cookie stickiness.

Note:

IP address-driven session persistence

Some products offer session persistence support without cookies. These products depend on the IP address of the incoming request. ISP proxies and company exit gateways can issue many requests from a single IP address. In this case, a single backend server can be subject to high traffic volumes. Your backend fleet can become overwhelmed, one server at a time, even though effective load balancing is possible.

Another weakness of IP address-driven session persistence is that the originating IP address can change. In this case, session persistence can be lost or the request redirected to the wrong backend server.

Application Cookie Stickiness

To configure application cookie session persistence, you only need to specify a cookie name. By default, traffic from a persistent session client is redirected to a different backend server when the original server is unavailable. This fallback behavior cannot be disabled.

The Load Balancing service activates application cookie session persistence (stickiness) when a backend server sends a Set-Cookie response header containing a recognized cookie name. The cookie name must match the name specified in the backend set configuration. If the configuration specifies a match-all pattern ( "*") any cookie set by the server activates session persistence. Unless a backend server activates session persistence, the service follows the load balancing policy specified when you created the load balancer.

Requirements:

  • The load balancer must operate in HTTP mode to support server side, cookie-driven session persistence.

  • The client computer must accept cookies for load balancing session persistence to work.

How It Works:

The Load Balancing service calculates a hash of the configured cookie and other request parameters, and sends that value to the client in a cookie. The value stored in the cookie enables the service to route subsequent client requests to the correct backend server. If your backend servers change any of the defined cookies, the service recomputes the cookie's value and resends it to the client.

Note:

Oracle recommends that you treat cookie data as an opaque entity. Do not use it in your applications.

The backend server can stop application cookie persistence by deleting the session persistence cookie. If you used the match-all pattern, it must delete all cookies. You can delete cookies by sending a Set-Cookie response header with a past expiration date. The Load Balancing service routes subsequent requests using the configured load balancing policy.

Load Balancer Cookie Stickiness

When you configure load balancer cookie stickiness, the load balancer inserts a cookie into the response. The parameters configured within the cookie enable session stickiness. This method is useful when you have applications and web backend services that cannot generate their own cookies.

To configure load balancer cookie session persistence, you specify these parameters and settings:

The cookie name

If you do not specify a cookie name, the default name is X-Oracle-BMC-LBS-Route.

Note:

Ensure that the cookie name used at the backend application servers is different from the cookie name used at the load balancer. To minimize the chance of name collision, Oracle recommends that you use a prefix such as X-Oracle-OCI-.

If both a backend server and the load balancer insert cookies with the same name, the client or browser behavior can vary depending on the domain value associated with the cookie. If the name and domain values of the Set-cookie header (generated by a backend server) and the Set-cookie header (generated by the load balancer) are the same, the client or browser treats them as one cookie. The client returns only one of the cookie values in subsequent requests. If both Set-cookie names are the same, but the domain names are different, the client or browser treats them as two different cookies.

The domain in which the cookie is valid

The Set-cookie header inserted by the load balancer contains a domain attribute with the specified value. This attribute has no default value. If you do not specify a value, the load balancer does not insert the domain attribute into the Set-cookie header.

Note:

  • RFC 6265 - HTTP State Management Mechanism describes client and browser behavior when the domain attribute is present or not present in the Set-cookie header.

    If the value of the Domain attribute is example.com in the Set-cookie header, the client includes the same cookie in the Cookie header when making HTTP requests to example.com, www.example.com, and www.abc.example.com. If the Domain attribute is not present, the client returns the cookie only for the domain to which the original request was made.

  • Ensure that this attribute specifies the correct domain value. If the Domain attribute in the Set-cookie header does not include the domain to which the original request was made, the client or browser might reject the cookie. As specified in RFC 6265, the client accepts a cookie with the Domain attribute value example.com or www.example.com sent from www.example.com. It does not accept a cookie with the Domain attribute abc.example.com or www.abc.example.com sent from www.example.com.

The URI path in which the cookie is valid

The Set-cookie header inserted by the load balancer contains a Path attribute with the specified value. Clients include the cookie in an HTTP request only if the path portion of the request-uri matches, or is a subdirectory of, the cookie's Path attribute. The default value is "/".

The amount of time the cookie remains valid

The Set-cookie header inserted by the load balancer contains a Max-Age attribute with the specified value. The specified value must be at least one second. No default value for this attribute exists. If you do not specify a value, the load balancer does not include the Max-Age attribute in the Set-cookie header. Usually, the client or browser retains the cookie until the current session ends, as defined by the client.

Whether the Set-cookie header should contain the Secure attribute

The Secure attribute directs the client or browser to send the cookie only using a secure protocol.

Note:

If you set this field to true, you cannot associate the corresponding backend set with an HTTP listener.

Whether the Set-cookie header should contain the HttpOnly attribute

The HttpOnly attribute limits the scope of the cookie to HTTP requests. This attribute directs the client or browser to omit the cookie when providing access to cookies through non-HTTP APIs. For example, it restricts the cookie from JavaScript channels.

Whether to disable fallback for unavailable servers
Refer to the "Fallback" section below.

Note:

Path route rules take precedence to determine the target backend server. The load balancer verifies that session stickiness is enabled for the backend server and that the cookie configuration is valid for the target. The system ignores invalid cookies.

Fallback

By default, the Load Balancing service directs traffic from a persistent session client to a different backend server when the original server is unavailable. You can configure the backend set to disable this fallback behavior. When you disable fallback, the load balancer fails the request and returns an HTTP 502 code. The service continues to return an HTTP 502 until the client no longer presents a persistent session cookie.

Caution:

If fallback is disabled, cookies with a distant future expiration date can cause a client outage.

Note:

The Load Balancing service considers a server marked drain available for existing persisted sessions. New requests that are not part of an existing persisted session are not sent to that server.