Using Shared Resources : Configuring health checks
 
Configuring health checks
In server load balancing deployments, the system uses health checks to poll the members of the real server pool to test whether an application is available. You can also configure additional health checks to poll related servers, and you can include results for both in the health check rule. For example, you can configure an HTTP health check test and a RADIUS health check test. In a web application that requires user authentication, the web server is deemed available only if the web server and the related RADIUS server pass the health check.
In link load balancing deployments, the health check can poll either the ISP link group member itself or a “beacon” server that is deployed on the other side of the ISP link. A beacon is an IP address that must be reachable in order for the link to be deemed available. A beacon can be any IP address, such as a main office, core router, or virtual server at another data center.
 
 
If you expect a backend server is going to be unavailable for a long period, such as when it is undergoing hardware repair, it is experiencing extended down time, or when you have removed it from the server farm, you can improve the performance of the FortiADC system by setting the status of the pool member to Disabled, rather than allowing the system to continue to attempt health checks.
Table 74 describes the predefined health checks. You can get started with these or create custom objects.
Table 74: Predefined health check configuration objects
Predefined
Description
LB_HLTHCK_HTTP
Sends a HEAD request to the server port 80. Expects the server to return an HTTP 200.
LB_HLTHCK_HTTPS
Sends a HEAD request to the server port 443. Expects the server to return an HTTP 200.
LB_HLTHCK_ICMP
Pings the server.
LB_HLTHCK_TCP_ECHO
Sends a TCP echo to server port 7. Expects the server to respond with the corresponding TCP echo.
Before you begin:
• You must have a good understanding of TCP/IP and knowledge of the services running on your backend servers.
• You must know the IP address, port, and configuration details for the applications running on backend servers. For some application protocol checks, you must specify user credentials.
• You must have Read-Write permission for Load Balance settings.
After you have configured a health check, you can select it in the real server configuration.
To configure a health check:
1. Go to System > Shared Resoures > Health Check.
2. Click Add to display the configuration editor.
3. Select one of the following options.
• ICMP
• TCP Echo
• TCP
• HTTP
• HTTPS
• DNS
• RADIUS
• SMTP
• POP3
• IMAP4
• RADIUS Accounting
• FTP
• TCP Half Open
• TCP SSL
• SNMP
• SSH
• L2 Detection
4. Complete the configuration as described in Table 75.
5. Save the configuration.
 
You can clone a predefined configuration object to help you get started with a user-defined configuration.
To clone a configuration object, click the clone icon that appears in the tools column on the configuration summary page.
 
Table 75: Health check configuration
Settings
Guidelines
General
Name
Configuration name. Valid characters are A-Z, a-z, 0-9, _, and -. No spaces.
After you initially save the configuration, you cannot edit the name.
Destination Address Type
• IPv4
• IPv6
Destination Address
IP address to send health check traffic.
In server load balancing deployments, if you do not specify an IP address, the real server IP address is used. You might configure IP address for a health check if you are configuring a combination of health checks to poll related servers.
In link load balancing deployments, if you do not specify an IP address, the destination IP address is the address of the gateway. You can configure IP address if you want to test connectivity to a beacon on the other side of the gateway, or if you want to test whether service traffic is allowed to pass through the link.
Interval
Seconds between each health check. Should be more than the timeout to prevent overlapping health checks. The default is 10.
Timeout
Seconds to wait for a reply before assuming that the health check has failed. The default is 5.
Up Retry
Attempts to retry the health check to confirm availability. The default is 1.
Down Retry
Attempts to retry the health check to confirm availability. The default is 1.
ICMP
No specific options
Simple ping to test connectivity.
TCP / TCP Half Open / TCP SSL
Port
Listening port number of the backend server. Usually HTTP is 80, FTP is 21, DNS is 53, POP3 is 110, IMAP4 is 143, RADIUS is 1812, and SNMP is 161.
HTTP/HTTPS
Port
Listening port number of the backend server. Usually HTTP is 80. If testing an HTTP proxy server, specify the proxy port.
HTTP CONNECT
If the real server pool members are HTTP proxy servers, specify an HTTP CONNECT option.
• Local CONNECT—Use HTTP CONNECT to test the tunnel connection through the proxy to the remote server. The member is deemed available if the request returns status code 200 (OK).
• Remote CONNECT—Use HTTP CONNECT to test both the proxy server response and remote server application availability. If you select this option, you can configure an HTTP request within the tunnel. For example, you can configure an HTTP GET/HEAD request to the specified URL and the expected response.
• No CONNECT—Do not use the HTTP CONNECT method. This option is the default. The HTTP CONNECT option is useful to test the availability of proxy servers only.
Remote Host
If you use HTTP CONNECT to test proxy servers, specify the remote server IP address.
Remote Port
If you use HTTP CONNECT to test proxy servers, specify the remote server port.
Method Type
HTTP method for the test traffic:
• HTTP GET—Send an HTTP GET request to the server. A response to an HTTP GET request includes HTTP headers and HTTP body.
• HTTP HEAD—Send an HTTP HEAD request. A response to an HTTP HEAD request includes HTTP headers only.
Send String
The request URL, such as /contact.php.
Receive String
A string expected in return when the HTTP GET request is successful.
Status Code
The health check sends an HTTP request to the server. Specify the HTTP status code in the server reply that indicates a successful test. Typically, you use status code 200 (OK). Other status codes indicate errors.
Match Type
What determines a failed health check?
• Match String
• Match Status
• Match All (match both string and status)
Not applicable when using HTTP HEAD. HTTP HEAD requests test status code only.
DNS
Domain Name
The FQDN, such as www.example.com, to use in the DNS A/AAAA record health check.
Address Type
• IPv4
• IPv6
Host Address
IP address that matches the FQDN, indicating a successful health check.
RADIUS / RADIUS Accounting
Port
Listening port number of the backend server. Usually RADIUS is 1812 and RADIUS accounting is 1813.
Username
User name of an account on the backend server.
Password
The corresponding password.
Password Type
• User—If the backend server does not use CHAP, select this option.
• CHAP—If the backend server uses CHAP and does not require a secret key, select this option.
Secret Key
The secret set on the backend server.
NAS IP Address
NAS IP address RADIUS attribute (if the RADIUS server requires this attribute to make a connection).
SMTP
Port
Listening port number of the backend server. Usually SMTP is 25.
Domain Name
The FQDN, such as www.example.com, to use in the SMTP HELO request used for health checks.
If the response is OK (250), the server is considered as up. If there is error response (501) or no response at all, the server is considered down.
POP3
Port
Listening port number of the backend server. Usually POP3 is 110.
Username
User name of an account on the backend server.
Password
The corresponding password.
IMAP4
Port
Listening port number of the backend server. Usually IMAP4 is 143.
Username
User name of an account on the backend server.
Password
The corresponding password.
Folder
Select an email mailbox to use in the health check. If the mailbox does not exist or is not accessible, the health check fails. The default is INBOX.
FTP
Port
Listening port number of the backend server. Usually FTP is 21.
User name
User name of an account on the backend server.
Password
The corresponding password.
File
Specify a file that exists on the backend server. Path is relative to the initial login path. If the file does not exist or is not accessible, the health check fails.
Passive
Select this option if the backend server uses passive FTP.
SNMP
Port
Listening port number of the backend server. Usually SNMP is 161 or 162.
CPU %
Maximum normal CPU usage. If overburdened, the health check fails.
Memory %
Maximum normal RAM usage. If overburdened, the health check fails.
Disk %
Maximum normal disk usage. If the disk is too full, the health check fails.
Agent type
• UCD
• Windows 2000
Community
The SNMP community string set on the backend server. If this does not match, and the appliance is not configured as an SNMP manager for the backend server, all SNMP health checks fail.
Version
SNMP v1 or v2c.
SSH
Port
Listening port number of the backend server. Usually SSH is 22.
Username
Username for test login.
Password
Corresponding password.
L2 Detection
No specific options
Link Layer health checker. Sends ARP (IPv4) or NDP (IPv6) packets to test whether a physically connected system is available.