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    Server Load Balancer:Add an HTTP listener

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    Server Load Balancer:Add an HTTP listener

    Last Updated:Apr 01, 2026

    HTTP listeners forward incoming HTTP traffic to your backend servers. Create an HTTP listener when your application — such as a web app or mobile game — needs to inspect and route HTTP requests.

    Prerequisites

    Before you begin, ensure that you have:

    Choose a creation method

    MethodWhen to use
    Manual creationConfigure advanced settings — timeouts, compression, header passthrough — based on your business requirements.
    Quick creationGet a listener running fast. Specify only the listener protocol, port, and server group.

    Manual creation

    1. Log on to the ALB console.

    2. In the top navigation bar, select the region where your ALB instance resides.

    3. Open the listener configuration wizard using one of the following methods:

      • On the Instances page, find your ALB instance and click Create Listener in the Actions column.

      • On the Instances page, click the ALB instance ID. On the Listener tab, click Create Listener.

    4. In the Configure Listener step, configure the parameters and click Next.

      ParameterDescription
      Listener protocolThe protocol for incoming requests. Select HTTP.
      Listener portThe port on which the ALB instance listens and forwards requests to backend servers. Valid values: 1–65535. Port 80 is standard for HTTP. On the same ALB instance, listeners using the same protocol must use unique ports, and HTTP listeners must use a different port than HTTPS listeners.
      Listener nameA name for the listener.
      TagKey-value pairs for filtering listeners. Add one or more tags.
      Advanced settingsClick Modify to configure the settings described below.

      Advanced settings

      SettingDescription
      Idle connection timeout periodHow long ALB waits before closing a connection with no activity. Unit: seconds. Valid values: 1–600. Default: 15. ALB closes the connection when the timeout expires and opens a new connection when the next request arrives. To set a longer timeout, go to the Quota Center console.
      Note

      Not available for HTTP/2 requests.

      Connection request timeoutHow long ALB waits for a backend server response before returning an HTTP 504 error to the client. Unit: seconds. Valid values: 1–600. Default: 60. To set a longer timeout, go to the Quota Center console.
      CompressionWhen enabled, ALB compresses responses where Content-Length exceeds 1,024 bytes. Brotli compresses all file types. GZIP compresses: text/xml, text/plain, text/css, application/javascript, application/x-javascript, application/rss+xml, application/atom+xml, application/xml, and application/json. When a client accepts both algorithms, ALB uses Brotli. When a client accepts only GZIP and any file type in the response is unsupported by GZIP, ALB skips compression entirely.
      Retrieve client IPRetrieve the source client IP address from the X-Forwarded-For header. Requires specifying trusted IP addresses. Set to 0.0.0.0/0 to treat the leftmost IP in the header as the client IP. Use the proxy1 IP;proxy2 IP;... format to compare IPs right-to-left — the first IP not on the trusted list is the client IP. Required for source IP matching and QPS-based throttling in forwarding rules. Available on standard and WAF-enabled ALB instances only.
      Add HTTP headerConfigure which headers ALB adds, preserves, or removes before forwarding requests. See the HTTP header reference below.

    5. In the Select server group step, select a server group, verify the backend servers, and click Next.

    6. In the Confirm step, review your configuration and click Submit.

    HTTP header reference

    X-Forwarded-For

    Important

    Use X-Forwarded-For with caution. Entries in this header are only trustworthy if they were added by properly secured systems. For guidance on preventing spoofing, see FAQ.

    When you select Add X-Forwarded-For to preserve client IP addresses, ALB can add or remove the header before forwarding requests. If you do not select this option, ALB passes the header through unchanged.

    The table below shows the X-Forwarded-For value that reaches your backend server for each scenario (example: last hop IP = 127.0.0.1).

    Incoming requestAdd (default)RemoveNot selected
    No X-Forwarded-For headerX-Forwarded-For: 127.0.0.1Header not presentHeader not present
    X-Forwarded-For: 127.0.0.2X-Forwarded-For: 127.0.0.2, 127.0.0.1Header not presentX-Forwarded-For: 127.0.0.2
    X-Forwarded-For: 127.0.0.2, 127.0.0.3X-Forwarded-For: 127.0.0.2, 127.0.0.3, 127.0.0.1Header not presentX-Forwarded-For: 127.0.0.2, 127.0.0.3

    • Add (default): ALB appends the last hop's IP to the header. If the request has no X-Forwarded-For header, ALB creates one with the last hop IP.

    • Remove: ALB strips the X-Forwarded-For header before forwarding.

    The header format is: X-Forwarded-For: <client-ip-address>, <proxy1>, <proxy2>, ...

    For a full guide on retrieving client IPs on backend servers, see Obtain client originating IP addresses on backend servers through an Application Load Balancer.

    Other headers

    HeaderWhat it stores
    SLB-IDThe ID of the ALB instance
    X-Forwarded-ProtoThe listener protocol
    X-Forwarded-PortThe listener port
    X-Forwarded-HostThe domain name of the client accessing ALB
    X-Forwarded-Client-srcportThe client port
    Note

    Configure your backend servers to process request headers case-insensitively, as required by the HTTP standard. ALB always creates X-Forwarded-For headers with an uppercase "X." For all other headers listed above, ALB follows the behavior described in this section. Any headers not listed here are forwarded in their original form.

    Quick creation

    1. Log on to the ALB console.

    2. In the top navigation bar, select the region where your ALB instance resides.

    3. On the Instances page, click your ALB instance ID.

    4. On the Listener tab, click Quick Create Listener.

    5. In the Quick Create Listener dialog box, configure the parameters and click OK.

      ParameterDescription
      Listener protocolThe protocol for incoming requests. Select HTTP.
      Listener portThe frontend port that receives and forwards requests to backend servers. Valid values: 1–65535.
      Resource groupThe resource group for the server group.
      Server groupSelect a backend server group type, then choose an existing server group with backend servers added, or create a new one.

    FAQ

    How can I prevent X-Forwarded-For header spoofing?

    The X-Forwarded-For header is easy to forge because clients control its initial value. Two approaches reduce this risk:

    • Use an upstream header for the real client IP. In a Client → CDN → WAF → SLB → ECS architecture, CDN records the real client IP in the Ali-Cdn-Real-Ip header. Configure WAF to use Ali-Cdn-Real-Ip as the client IP detection field. On your backend Nginx server, log $http_Ali_Cdn_Real_Ip as the real client IP.

    • Switch to a layer 4 listener (NLB or CLB). Layer 4 listeners pass the real client IP directly to backend servers without relying on X-Forwarded-For. See Enable layer 4 listeners to preserve client IP addresses and pass them to backend servers.

    Does ALB support the WebSocket protocol?

    ALB HTTP listeners support WebSocket by default. See Use WebSocket to enable real-time messaging.

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