Applies To:
Show Versions
3-DNS Controller versions 1.x - 4.x
- 4.1.1, 4.1.0
5
Load Balancing
- Working with load balancing modes
- Understanding load balancing
- Configuring load balancing
- Changing global variables that affect load balancing
- Troubleshooting manual configuration problems
Working with load balancing modes
Load balancing modes are used by the 3-DNS Controller to distribute the DNS name resolution requests, sent by local DNS servers, to the best available virtual server in your network. This chapter first describes how load balancing works on the 3-DNS Controller, explains the various static and dynamic load balancing modes, and then describes how to configure them.
Understanding load balancing
When the 3-DNS Controller receives a name resolution request from a local DNS server, the controller uses a load balancing mode to select the best available virtual server from a wide IP pool. Once the 3-DNS Controller selects the virtual server, it constructs the DNS answer (either an A record for each virtual server IP address, an NS record, or a CNAME record) and sends the answer back to the requesting client's local DNS server.
The 3-DNS Controller can choose a virtual server from a wide IP pool using either a static load balancing mode, which selects a server based on a pre-defined pattern, or an dynamic load balancing mode, which selects a server based on current performance.
The 3-DNS Controller uses load balancing modes in two situations:
- Load balancing among multiple pools
The 3-DNS Controller supports multiple pools. Configurations that contain two or more pools use a load balancing mode first to select a pool. Once the 3-DNS Controller selects a pool, the controller then uses a load balancing mode to choose a virtual server, within the selected pool. If the controller does not choose a virtual server in the first pool, it applies the load balancing mode to a different pool, either until it selects a virtual server, or all the pools are tried. - Load balancing within a pool
Within each pool, you specify three different load balancing modes that the controller uses in sequential order: preferred method, alternate method, and fallback method. The preferred method is the first load balancing mode that the 3-DNS Controller uses for load balancing. If the preferred method fails, the controller then uses the alternate method for load balancing. If this load balancing mode fails, the controller uses the fallback load balancing mode. If the fallback method fails, the 3-DNS Controller returns the client to standard DNS for resolution.
Table 5.1 shows a complete list of supported load balancing modes, and indicates where you can use each mode in the 3-DNS Controller configuration. The following sections in this chapter describe how each load balancing mode works.
Using static load balancing modes
Static load balancing modes distribute connections across the network according to predefined patterns, and take server availability into account. The 3-DNS Controller supports the following static load balancing modes:
- Static Persist
- Round Robin
- Ratio
- Random
- Global Availability
- Topology
- None
- Return to DNS
The None and Return to DNS load balancing modes are special modes that you can use to skip load balancing under certain conditions. The other static load balancing modes perform true load balancing as described in the following sections.
Static Persist mode
Static Persist mode provides static persistence of local DNS servers to virtual servers; it consistently maps an LDNS IP address to the same available virtual server for the duration of the session. This mode guarantees that certain transactions will be routed through a single transaction manager (for example, a BIG-IP Controller or other server array controller); this is beneficial for transaction-oriented traffic such as e-commerce shopping carts or online trading.
Round Robin mode
Round Robin mode distributes connections in a circular and sequential pattern among the virtual servers in a pool. Over time, each virtual server receives an equal number of connections.
Figure 5.1 shows a sample of the connection distribution pattern for Round Robin mode.
Ratio mode
Ratio mode distributes connections among a pool of virtual servers as a weighted Round Robin. For example, you can set up Ratio mode to send twice as many connections to a fast, new server, and only half as many connections to an older, slower server.
This load balancing mode requires that you define a ratio weight for each virtual server in a pool, or for each pool if you are using Ratio mode to load balance among multiple pools. The default ratio weight for a server or a pool is set to 1.
Figure 5.2 shows a sample connection distribution for Ratio mode.
Random mode
Random mode sends connections to virtual servers in a random, uniform distribution pattern. The Random mode is useful for certain test configurations.
Global Availability mode
Global Availability mode uses the virtual servers included in the pool in the order in which they are listed. For each connection request, this mode starts at the top of the list and sends the connection to the first available virtual server in the list. Global Availability mode moves to the next virtual server in the list only when the current virtual server is full or otherwise unavailable. Over time, the first virtual server in the list receives the most connections and the last virtual server in the list receives the least number of connections.
Topology mode
Topology allows you to direct or restrict traffic flow by entering network information into a topology statement in the configuration file. This allows you to develop proximity-based load balancing. For example, client requests in a particular geographic region can be directed to servers within that same region. The 3-DNS Controller determines the proximity of servers by comparing location information derived from the DNS message to the topology records.
This load balancing mode requires you to do some advanced configuration planning, such as gathering the information you need to define the topology records that determine proximity of client local DNS servers to the various virtual servers. The 3-DNS Controller contains an IP classifier that accurately maps local DNS servers, so when you create topology records, you can refer to continents and countries, instead of IP subnets.
See Chapter 11, Topology , for detailed information about working with this and other topology features. For an example configuration using the Topology load balancing mode, see Chapter 3, Configuring a Globally-Distributed Network, in the 3-DNS Administrator Guide.
None mode
The None load balancing mode is a special mode you can use if you want to skip the current load balancing method, or skip to the next pool in a multiple pool configuration. For example, if you set an alternate method to None in a pool, the 3-DNS Controller skips the alternate method and immediately tries the load balancing mode specified as the fallback method. If the fallback method is set to None, and you have multiple pools configured, the 3-DNS Controller uses the next available pool. If you do not have multiple pools configured, the contoller returns the connection request to DNS for resolution.
This mode is most useful for multiple pool configurations. For example, you can temporarily remove a specific pool from service by setting each of the methods (preferred, alternate, and fallback) to None. (Note that you can also disable a pool from the Modify Wide IP Pools screen, in the Configuration utility.) You could also use the mode to limit each pool to a single load balancing mode. For example, you would set the preferred method in each pool to the desired load balancing mode, and then you would set both the alternate and fallback methods to None in each pool. If the preferred method fails, the None mode in both the alternate and fallback methods forces the 3-DNS Controller to go to the next pool for a load balancing answer.
Return to DNS mode
The Return to DNS mode is another special load balancing mode that you can use to immediately return connection requests to DNS for resolution. This mode is particularly useful if you want to temporarily remove a pool from service, or if you want to limit a pool in a single pool configuration to only one or two load balancing attempts.
Using dynamic load balancing modes
Dynamic load balancing modes distribute connections to servers that show the best current performance. The performance metrics taken into account depend on the particular dynamic mode you are using.
All dynamic load balancing modes make load balancing decisions based on the metrics collected by the big3d agents running in each data center. The big3d agents collect the information at set intervals that you define when you set the global timer variables. If you want to use the dynamic load balancing modes, you must run one or more big3d agents in each of your data centers, to collect the required metrics.
The 3-DNS Controller supports the following dynamic load balancing modes:
- Completion Rate
- Least Connections
- Packet Rate
- Round Trip Times (RTT)
- Hops
- Kilobytes/Second
- Quality of Service (QOS)
- VS Capacity
Completion Rate mode
Completion Rate mode selects a virtual server that currently maintains the least number of dropped or timed-out packets during a transaction between a data center and the client LDNS.
Figure 5.3 shows a sample connection distribution pattern for Completion Rate mode.
Figure 5.3 Completion Rate load balancing mode
Least Connections mode
Least Connections mode is used for load balancing virtual servers managed by BIG-IP Controllers. Least Connections mode simply selects a virtual server on the BIG-IP Controller that currently hosts the fewest connections.
Packet Rate mode
Packet Rate mode selects a virtual server that is currently processing the fewest number of packets per second.
Figure 5.4 shows a sample connection distribution for Packet Rate mode.
Round Trip Times mode
Round Trip Times (RTT) mode selects the virtual server with the fastest measured round trip time between the data center and the client LDNS.
Figure 5.5 shows a sample connection distribution for Round Trip Times mode.
Figure 5.5 Round Trip Times mode
Hops mode
Hops mode is based on the traceroute utility, and it tracks the number of intermediate system transitions (hops) between the client LDNS and each data center. Hops mode selects a virtual server in the data center that has the fewest network hops from the LDNS.
Kilobyte/Second mode
Kilobytes/Second mode selects a virtual server that is currently processing the fewest number of kilobytes per second.
Quality of Service mode
Quality of Service mode uses the current performance information, calculates an overall score for each virtual server, and then distributes connections based on each virtual server's score. The performance factors that it takes into account include:
- Round trip time
- Hops
- Completion rate
- Packet rate
- Topology
- VS Capacity
- Kilobytes/Second
Quality of Service mode is a customizable load balancing mode. For simple configurations, you can easily use this mode with its default settings. For more advanced configurations, you can specify different weights for each performance factor in the equation.
You can also configure the Quality of Service load balancing mode to use the dynamic ratio feature. With the dynamic ratio feature turned on, the Quality of Service mode becomes similar to the Ratio mode where the connections are distributed in proportion to ratio weights assigned to each virtual server. The ratio weights are based on the QOS scores: the better the score, the higher percentage of connections the virtual server receives.
For details about customizing Quality of Service mode, see Setting up Quality of Service (QOS) mode in Chapter 7 of the 3-DNS Administrator Guide.
VS Capacity mode
VS Capacity mode selects the virtual server that has the most nodes up. If more than one virtual server has the same quantity of nodes up, then the 3-DNS Controller load balances using the Random mode among those virtual servers.
Configuring load balancing
This section describes how to configure load balancing on the 3-DNS Controller. You configure load balancing at both the global and wide IP levels:
- Global
At the global level, you can configure default settings for the alternate and fallback load balancing methods. Then, if you do not specify alternate or fallback modes when defining a wide IP, the 3-DNS Controller uses the alternate and fallback methods you have configured at the global level. You can find instructions on how to configure global alternate and fallback methods in Setting global alternate and fallback methods, on page 5-16 . - Wide IP
When defining a wide IP, if you have multiple pools in your wide IP, you first specify which load balancing mode to use in selecting the pool in the wide IP. Next, you specify which preferred, alternate, and fallback load balancing methods to use in selecting the virtual server within the selected pool. You can find instructions on how to configure these load balancing methods in the section, Defining a wide IP, on page 5-12 .
Understanding wide IPs
After you configure the BIG-IP Controllers, EDGE-FX Caches, hosts, and the virtual servers they manage, you need to group the configured virtual servers into a wide IP. A wide IP is a mapping of a fully-qualified domain name (FQDN) to a set of virtual servers that host the domain content, such as a web site, an e-commerce site, or a CDN.
Before defining the first wide IP, you should do the following:
- Gather your configuration information for the BIG-IP Controller, EDGE-FX Cache, and host so you can easily see which virtual servers have the content you want to map to an FQDN. Then you can decide how to group virtual servers into pools.
- Decide which load balancing modes to use for each pool of virtual servers.
Note: NameSurfer, an application included with the 3-DNS Controller, sets up DNS zone files so that wide IP definitions are properly linked to DNS. NameSurfer registers the virtual servers you add to wide IP pools as A records. No action is required on your part, as NameSurfer automatically handles this process. For more information on NameSurfer, see the online help that is included with it (available from the Configuration utility).
There may be situations (for example, e-commerce, and other sites with multiple services) where you need to configure a wide IP so that connections are not sent to a given address unless multiple ports or services are available. You configure this behavior after you define the wide IP. For details, see Setting up load balancing for services that require multiple ports, in Chapter 7 of the 3-DNS Administrator Guide.
Understanding pools
A wide IP contains one or more pool definitions. A pool is a group of virtual servers that the 3-DNS Controller load balances. You can include all types of virtual servers (BIG-IP Controller, EDGE-FX Cache, and host) in a pool definition.
Defining a wide IP
After you determine which virtual servers you should place in which wide IP pools, you are ready to add the first wide IP to the configuration.
To define a wide IP using the Configuration utility
- In the navigation pane, click Wide IPs.
The Wide IP List screen opens. - On the toolbar, click Add Wide IP.
The Add a New Wide IP screen opens. - Add the wide IP settings. For help on defining wide IPs, click Help on the toolbar.
The wide IP is added to your configuration.Repeat this process for each wide IP you want to add.
To define a wide IP from the command line
- At the command prompt, type 3dnsmaint to open the 3-DNS Maintenance menu.
- On the 3-DNS Maintenance menu, choose Edit 3-DNS Configuration to open the wideip.conf file.
- Add a wideip statement.
Place the wideip statement after all server statements and before any topology statement.
- Under the wideip statement, enter the wide IP address, port, and name information. Enclose the wide IP name in quotation marks.
- Configure any options you want to set (such as the TTL, port list, or QOS coefficients) by entering the appropriate sub-statements.
- Define the pool sub-statement. At the minimum, the pool sub-statement should include its name (enclosed in quotation marks) and the virtual servers it contains.
- Define the load balancing modes you want to use by entering preferred, alternate, and fallback sub-statements.
- Define the IP address, port, and ratio value for each virtual server that you want to include in this pool.
Figure 5.6 shows the correct syntax for the wideip statement.
Figure 5.6 Syntax for the wideip statement
wideip {
address <ip_addr>
port <port_number> | <"service name">
persist < yes | no >
persist_ttl <number>
name <"domain_name">
[ alias <"alias_name"> ]
[ ttl <number> ]
[ port_list <port_number> <port_number> ... ]
[ qos_coeff {
rtt <n>
completion_rate <n>
packet_rate <n>
topology <n>
hops <n>
vs_capacity <n>
kbps <n>
} ]
[ pool_lbmode <rr | ratio | ga | random | topology> ]
pool {
name <"pool_name">
[ limit {
kbytes_per_second
pkts_per_second <number>
current_conns <number>
cpu_usage <number>
mem_avail <number>
disk_avail <number>
}]
[ ratio <pool_ratio> ]
[ dynamic_ratio < yes | no > ]
[ rr_ldns < yes | no > ]
[ preferred < completion_rate | ga | hops | kbps | leastconn | packet_rate | qos | random | ratio | return_to_dns | rr | rtt | topology | null | vs_capacity | static_persist> ]
[ alternate < ga | null | random | ratio | return_to_dns | rr | topology | vs_capacity | static_persist> ]
[ fallback <completion_rate | ga | hops | leastconn | null | packet_rate | qos | random | ratio | return_to_dns | rr | rtt | topology | vs_capacity | static_persist> ]
address <vs_addr>[:<port>] [ratio <weight>]
address <vs_addr>[:<port>] [ratio <weight>]
address <vs_addr>[:<port>] [ratio <weight>]
...
}
}
An example of the wideip statement
Figure 5.7 shows a sample wideip statement. This statement defines a wide IP named mx.wip.domain.com, with an alias of mail.wip.domain.com. The wide IP contains two pools, with pool_1 receiving three times as many requests as pool_2. The 3-DNS Controller attempts to resolve requests sent to pool_1 using the Round Trip Times (RTT) mode. This mode sends connections to the virtual server in the pool that demonstrates the best round trip time between the virtual server and the client LDNS. If the 3-DNS Controller cannot resolve the request using the RTT mode, the controller distributes requests using the Random load balancing mode. The 3-DNS Controller distributes requests at a 2:1 ratio to the two virtual servers defined in pool_2, where the first listed virtual server receives twice as many connections as the second.
Figure 5.7 Example syntax for defining a wide IP
wideip {
address 192.168.102.50
service "smtp"
name "mx.wip.domain.com"
alias "mail.wip.domain.com"
pool_lbmode ratio
pool {
name "pool_1"
ratio 3
preferred rtt
alternate random
address 192.168.101.50
address 192.168.102.50
address 192.168.103.50
}
pool {
name "pool_2"
ratio 1
preferred ratio
address 192.168.104.50 ratio 2
address 192.168.105.50 ratio 1
}
}
Using the LDNS round robin wide IP attribute
LDNS round robin is an attribute that you can use in conjunction with any load balancing mode. The LDNS round robin attribute allows the 3-DNS Controller to return a list of available virtual servers, instead of a single virtual server. Certain browsers keep the answer returned by DNS servers. By enabling this attribute, the 3-DNS Controller returns a maximum of 16 virtual servers as the answer to a DNS resolution request. This provides browsers with alternate answers if a virtual server becomes unavailable.
Using the last resort pool designation
The last resort pool is an optional setting for a wide IP pool. The wide IP pool that you designate as the last resort pool, in the Configure Load Balancing for New Pool screen, is the virtual server pool that the 3-DNS Controller uses when all other pools have reached their thresholds or are unavailable for any reason. The 3-DNS Controller uses the last resort pool only when it tries, unsuccessfully, to load balance to all other configured pools
When your network includes cache appliances hosting content from an origin site, you can designate the origin site as the last resort pool to handle requests if your cache virtual servers have reached their thresholds. You can also use the last resort pool to designate an overflow network so your origin servers remain available if network traffic spikes. You can only designate one last resort pool within a wide IP.
To designate a last resort pool using the Configuration utility
- In the navigation pane, select Wide IPs.
The Wide IP List screen opens. - From the Pools column, select the pools for the wide IP for which you want to create a last resort pool.
The Modify Wide IP Pools screen opens. - From the Pool Name column, click the pool that you want to designate as the last resort pool.
The Modify Load Balancing for [pool name] screen opens. - Check the box next to Last Resort Pool, and click Update.
To designate a last resort pool from the command line
In the wideip.conf file, change the last_resort definition from no to yes for the pool that you want to designate as the last resort pool. Figure 5.8 shows an example of a last resort pool definition.
Figure 5.8 Example of a last resort pool definition
pool {
name "origin"
last_resort yes
preferred kbps
alternate rr
fallback return_to_dns
address 192.168.103.5
address 192.168.103.6
address 192.168.103.7
}
Changing global variables that affect load balancing
You can configure global variables that affect how load balancing is handled on a global basis for all wide IPs managed by the 3-DNS Controller. You can override these global settings for individual wide IPs as necessary.
Global variables that affect load balancing fall into two categories:
- Alternate and fallback load balancing methods
- TTL (time to live) and timer values
The default settings for these variables are adequate for most configurations. However, if you want to change any global variable, you should refer to the online help.
Setting global alternate and fallback methods
You can configure a load balancing method that all wide IPs can use in the event that their preferred method fails.
To configure global alternate and fallback load balancing methods using the Configuration utility
- In the navigation pane, click System.
The System - General screen opens. - On the toolbar, click Load Balancing.
- In the Default Alternate box, select the load balancing mode to use should a wide IP's preferred method fail.
- In the Default Fallback box, specify the load balancing mode to use should the preferred and alternate methods fail.
If all methods fail, requests are returned to DNS. - Finish configuring the rest of the settings on the System - Load Balancing screen. (For help on configuring the load balancing settings, click Help on the toolbar.)
The global load balancing settings are added to your configuration.
To configure global alternate and fallback load balancing methods from the command line
- At the command prompt, type 3dnsmaint to open the 3-DNS Maintenance menu.
- On the 3-DNS Maintenance menu, choose Edit 3-DNS Configuration to open the wideip.conf file.
- Locate or add the globals statement. The globals statement should be at the top of the file.
- Use the syntax shown in Figure 5.9 to define global alternate and fallback load balancing methods.
Figure 5.9 Configuring global alternate and fallback load balancing modes
globals {
[ default_alternate < ga | leastconn | null | packet_rate | random | ratio | return_to_dns | rr | topology | static_persist | vs_capacity > ]
[ default_fallback < completion_rate | ga | hops | leastconn | null | packet_rate | qos | random | ratio | return_to_dns | rr | rtt | topology | static_persist | vs_capacity> ]
}Figure 5.10 shows a sample globals statement that defines global load balancing variables.
Figure 5.10 Sample syntax for setting global load balancing variables
globals {
default_alternate leastconn
default_fallback rr
}
Understanding TTL and timer values
Each 3-DNS object has an associated time-to-live (TTL) value. A TTL is the amount of time (measured in seconds) for which metrics information is considered valid. The timer values determine how often the 3-DNS Controller refreshes the information.
Table 5.2 describes each TTL value, as well as its default setting.
Each 3-DNS object also has a timer value. A timer value defines the frequency (measured in seconds) at which the 3-DNS Controller refreshes the metrics information it collects. In most cases, the default values for the TTL and timer parameters are adequate. However, if you make changes to any TTL or timer value, keep in mind that an object's TTL value must be greater than its timer value.
Table 5.3 describes each timer value, as well as its default setting.
To configure global TTL and timer values using the Configuration utility
- In the navigation pane, click System.
The System - General screen opens. - To configure the default TTL for wide IPs, type a new value in the Default TTL box.
- To configure other TTL and timer values, click Timers and Task Intervals on the toolbar.
The System - Timers & Task Intervals screen opens. - Add the TTL and timer values settings.
For help on configuring the TTL and timer values settings, click Help on the toolbar.
To configure global TTL and timer values from the command line
- At the command prompt, type 3dnsmaint to open the 3-DNS Maintenance menu.
- On the 3-DNS Maintenance menu, choose Edit 3-DNS Configuration to open the wideip.conf file.
- Locate or add the globals statement. The globals statement should be at the top of the file.
- Use the syntax shown in Figure 5.11 to define global TTL and timer values.
Figure 5.11 Syntax for configuring global TTL and timer values
globals {
[ timer_get_3dns_data <number> ]
[ timer_get_server_data <number> ]
[ timer_get_host_data <number> ]
[ timer_get_vs_data <number> ]
[ timer_get_ecv_data <number> ]
[ timer_get_path_data <number> ]
[ timer_get_trace_data <number> ]
[ timer_check_keep_alive <number> ]
[ timer_check_pending_q_timeouts <number> ]
[ timer_persist_cache <number> ]
[ timer_sync_state <number> ]
[ 3dns_ttl <number> ]
[ server_ttl <number> ]
[ host_ttl <number> ]
[ vs_ttl <number> ]
[ path_ttl <number> ]
[ trace_ttl <number> ]
[ default_ttl <number> ]
}
Troubleshooting manual configuration problems
Adding a wide IP requires careful planning and use of correct syntax. We recommend using the Configuration utility to create wide IPs and pools so that the correct syntax is generated automatically in the wideip.conf file. However, we have included the following recommendations to make it easier for you to spot and resolve any configuration problems if you choose to create your configuration by editing the wideip.conf file.
- Configuration utility
The Configuration utility contains Statistics screens that are useful in diagnosing problems, as they provide a snapshot of the 3-DNS Controller network at any given time. To use them, expand the Statistics item in the navigation pane, then click either Wide IPs or Summary (and scroll until you see the Wide IP table).
The Configuration utility also contains the Network Map, which allows you to see the relationships between your data centers, servers, and virtual servers, and the wide IPs and pools you created with the virtual servers. For information on working with the Network Map, click Help on the toolbar. - wideip.conf syntax
If you configure wide IPs from the command line, use the 3dparse utility to verify wideip.conf syntax before you start 3dnsd. To use this utility, type 3dparse on the command line. For details on the 3dparse utility, see the 3dparse man page. - /var/log/messages
If you encounter an error that you cannot trace, you can view the log file in the Configuration utility, or you can directly open the /var/log/messages file on your system. Using the UNIX grep utility, search for 3dnsd (for example, tail -100 /var/log/messages | grep 3dnsd). This log file saves verbose error information, and should contain an explanation of the error. - BIND syntax
If you are setting up the configuration from the command line, you may want to refer to one of the following BIND resources for help and background information:
- The O'Reilly & Associates book, DNS and BIND, Third Edition
- http://www.isc.org/bind.html
