Manual Chapter :
Global Server Load Balancing
Applies To:
Show VersionsBIG-IP DNS
- 17.1.1, 17.1.0, 17.0.0, 16.1.5, 16.1.4, 16.1.3, 16.1.2, 16.1.1, 16.1.0, 16.0.1, 16.0.0, 15.1.10, 15.1.9, 15.1.8, 15.1.7, 15.1.6, 15.1.5, 15.1.4, 15.1.3, 15.1.2, 15.1.1, 15.1.0, 15.0.1, 15.0.0
Global Server Load Balancing
Introducing BIG-IP DNS
BIG-IP DNS (formerly GTM™) is a system that monitors
the availability and performance of global resources and uses that information to manage network
traffic patterns. BIG-IP DNS uses load balancing algorithms, topology-based routing, and iRules® to control and distribute traffic according to specific policies.
About global server
load balancing
BIG-IP DNS provides tiered global
server load balancing (GSLB). BIG-IP DNS distributes DNS name resolution requests, first to the
best available pool in a wide IP, and then to the best available virtual server within that pool.
BIG-IP DNS selects the best available resource using either a static or a dynamic load balancing
method. Using a static load balancing method, BIG-IP DNS selects a resource based on a
pre-defined pattern. Using a dynamic load balancing method, BIG-IP DNS selects a resource based
on current performance metrics collected by the
big3d
agents running in each data center. Static load balancing methods
This table describes the static load balancing methods available in BIG-IP DNS.
Name |
Description |
Recommended Use |
Wide IP Load Balancing |
Preferred Method |
Alternate Method |
Fallback Method |
---|---|---|---|---|---|---|
Drop Packet |
BIG-IP DNS drops the DNS request. |
Use Drop Packet for the Alternate
load balancing method when you want to ensure that BIG-IP DNS does not offer in a
response a virtual server that is potentially unavailable. |
No |
Yes |
Yes |
Yes |
Fallback IP |
BIG-IP DNS distributes DNS name resolution requests to a virtual server that you
specify. This virtual server is not monitored for availability. |
Use Fallback IP for the fallback load balancing method
when you want BIG-IP DNS to return a disaster recovery site when the preferred and
alternate load balancing methods do not return an available virtual server. |
No |
No |
No |
Yes |
Global Availability |
BIG-IP DNS distributes DNS name resolution requests to the first available
virtual server in a pool. BIG-IP DNS starts at the top of a manually configured list
of virtual servers and sends requests to the first available virtual server in the
list. Only when the virtual server becomes unavailable does BIG-IP DNS send requests
to the next virtual server in the list. Over time, the first virtual server in the
list receives the most requests and the last virtual server in the list receives the
least requests. |
Use Global Availability when you have specific virtual
servers that you want to handle most of the requests. |
Yes |
Yes |
Yes |
Yes |
None |
BIG-IP DNS distributes DNS name resolution requests skipping either the next
available pool in a multiple pool configuration or the current load balancing method.
If all pools are unavailable, BIG-IP DNS returns an aggregate of the IP addresses of
all the virtual servers in the pool using BIND. |
Use None for the alternate and fallback methods when you
want to limit each pool to a single load balancing method. If the preferred load
balancing method fails, BIG-IP DNS offers the next pool in a load balancing response. |
No |
No |
Yes |
Yes |
Ratio |
BIG-IP DNS distributes DNS name resolution requests among the virtual servers in
a pool or among pools in a multiple pool configuration using weighted round
robin , a load balancing pattern in which requests are distributed among
several resources based on a priority level or weight assigned to each resource. |
Use Ratio when you want to send twice as many connections
to a fast server and half as many connections to a slow server. |
Yes |
Yes |
Yes |
Yes |
Return to DNS |
BIG-IP DNS immediately distributes DNS name resolution requests to an LDNS for
resolution. |
Use Return to DNS when you want to temporarily remove a
pool from service. You can also use Return to DNS when you want
to limit a pool in a single pool configuration to only one or two load balancing
attempts. |
No |
Yes |
Yes |
Yes |
Round Robin |
BIG-IP DNS distributes DNS name resolution requests in a circular and sequential
pattern among the virtual servers in a pool. Over time each virtual server receives an
equal number of requests. |
Use Round Robin when you want to distribute requests
equally among all virtual servers in a pool. |
Yes |
Yes |
Yes |
Yes |
Static Persist |
BIG-IP DNS distributes DNS name resolution requests to the first available
virtual server in a pool using the persist mask with the source IP address of the LDNS
and a hash algorithm to determine the order of the virtual servers in the list. This
hash algorithm orders the virtual servers in the list differently for each LDNS that
is passing traffic to the system taking into account the specified CIDR of the LDNS.
Each LDNS (and thus each client) generally resolves to the same virtual server;
however, when the selected virtual server becomes unavailable, BIG-IP DNS sends
requests to another virtual server until the original virtual server becomes
available. Then BIG-IP DNS again resolves requests to that virtual server. |
Use Static Persist when you want requests from a specific
LDNS to resolve to a specific virtual server. |
No |
Yes |
Yes |
Yes |
Topology |
BIG-IP DNS distributes DNS name resolution requests using proximity-based load
balancing. BIG-IP DNS determines the proximity of the resource by comparing location
information derived from the DNS message to the topology records in a topology
statement you have configured. |
Use Topology when you want to send requests from a client
in a particular geographic region to a data center or server located in that
region. |
Yes |
Yes |
Yes |
Yes |
Dynamic load balancing methods
This table describes the dynamic load balancing methods available in BIG-IP
DNS.
Name |
Description |
Wide IP load balancing |
Preferred method |
Alternate method |
Fallback method |
---|---|---|---|---|---|
Completion Rate |
BIG-IP
DNS distributes DNS name resolution requests to the virtual
server that currently maintains the least number of dropped or timed-out packets
during a transaction between a data center and the client's LDNS. |
No |
Yes |
No |
Yes |
CPU |
BIG-IP DNS distributes DNS name resolution requests to the virtual server that
currently has the most CPU processing time available. |
No |
Yes |
No |
Yes |
Hops |
BIG-IP DNS distributes DNS name resolution requests to a virtual server in the
data center that has the fewest router hops from the client's LDNS. BIG-IP DNS uses
the traceroute utility to track the number of router hops between a client's LDNS and
each data center. |
No |
Yes |
No |
Yes |
Kilobytes/Second |
BIG-IP DNS distributes DNS name resolution requests to the virtual server that is
currently processing the fewest number of kilobytes per second. Use
Kilobytes/Second only with virtual servers for which BIG-IP
DNS can collect the kilobytes per second metric. |
No |
Yes |
No |
Yes |
Least Connections |
BIG-IP DNS distributes DNS name resolution requests to virtual servers on BIG-IP
Local Traffic Manager (LTM) that currently
hosts the fewest connections. Use Least Connections only with
LTM servers. |
No |
Yes |
No |
Yes |
Packet Rate |
BIG-IP DNS distributes DNS name resolution requests to the virtual server that is
currently processing the fewest number of packets per second. |
No |
Yes |
Yes |
Yes |
Quality of Service |
BIG-IP DNS distributes DNS name resolution requests to virtual servers based on a
score assigned to each virtual server that is calculated from current performance
metrics. Use Quality of Service only when you have configured
BIG-IP DNS to calculate an overall score for each virtual server based on performance
metrics. |
No |
Yes |
No |
Yes |
Round Trip Time |
BIG-IP DNS distributes DNS name resolution requests to the virtual server with
the fastest measured round trip time between a data center and a client's
LDNS. |
No |
Yes |
No |
Yes |
Virtual Server Score |
BIG-IP DNS distributes DNS name resolution requests to virtual servers on LTM
based on a user-defined ranking. Use Virtual Server Score only
with LTM systems on which you have assigned scores to each virtual server. |
No |
Yes |
Yes |
Yes |
Virtual Server Capacity |
BIG-IP DNS distributes DNS name resolution requests to virtual servers in a list
that are weighted by the number of available virtual servers in the pool. Use
Virtual Server Capacity for load balancing virtual servers
managed by LTM Systems. BIG-IP DNS selects a virtual server that has the most available (UP)
members. When selecting a virtual server from a wide IP pool and two or more virtual
servers result in equal scores, BIG-IP DNS will return one of the equal scored virtual
servers randomly. |
No |
Yes |
Yes |
Yes |