Shulou(Shulou.com)06/01 Report--

When building data centers, enterprises will build two or more data centers for the sake of disaster preparedness. For example, we often talk about "two places and three centres", that is, double centres in the same city + non-local centres.

Dual centers in the same city refers to the establishment of two data centers that can undertake business independently in the same city or neighboring cities. The two centers have basically the same business processing capacity and synchronize data in real time through high-speed links. Under daily circumstances, the operation of the business and management system can be shared at the same time, and can be switched; emergency switching should be prepared in case of disaster to ensure the continuity of the business. Remote disaster preparedness center refers to the establishment of a backup disaster preparedness center in remote cities for dual-center data backup. When the two centers fail due to natural disasters and other reasons, remote disaster preparedness centers can use backup data for business recovery.

Today, we mainly talk about the network deployment model, switching mode, advantages and disadvantages of dual-center in the same city.

The deployment of dual centers in the same city can be divided into two ways, namely, active / standby and dual-active.

1. Active and standby center model

Literally, the main and standby center is the construction of two data centers, one master and one standby, both of which have the ability to provide services independently. Under normal circumstances, the main center provides services to the outside. When a major failure occurs, the business of the main center is switched to the standby center, and the standby center becomes a new production center to provide services.

The above description of the master / standby relationship is very simple, but in the actual deployment process, we need the coordination and cooperation of network, application, database and other departments to switch. Today, we are mainly talking about the network.

Schematic diagram of active and standby data centers:

The figure above shows a typical network model of master and slave centers in the same city. Center An is the production center, Center B is the standby center, and the business zones of Center An and Center B use the same IP address range.

The technical key points of this model:

1. The network core (gateway) of Center An and B will be connected at layer 2.

two。 The gateway is enabled on the side of the main center, and the standby center gateway is closed.

3. Main center A publishes routes, while center B does not issue routes.

Switching between data centers:

The A center stops issuing routes to the outside world, and the B center, while switching the gateway of the A center to the B center, thus completing the switching of the data center network.

Advantages of active and standby models:

1. The technology is simple and convenient to switch.

two。 The transition from the existing dual-center to this model is simple and does not involve the application of IP address transformation.

Disadvantages of active and standby models:

1. There is a lot of cross-center traffic, so it is impossible to "get in and out of the center server from the center" (the gateways on both sides cannot be turned on at the same time, otherwise there will be firewall asynchronous routing problems).

two。 The physical distance between centers is too long, resulting in increased network latency, which may affect delay-sensitive applications.

3. The L2 connection between centers will expand the layer 2 domain, and the layer 2 failure of one center may affect another center, which requires data center STP isolation or the use of special technologies, such as OTV

4. The problem of how to synchronize firewall policies should be considered.

5. The link is idle and the resources are not maximized, such as the WAN link outside the B center.

two。 Double active center model

Dual active data centers, that is, two data centers have the ability to provide services at the same time. As shown below:

Two data centers An and B use independent IP address segments and provide services to the outside at the same time. The client relies on the parsing results of DNS to determine which data center to enter from.

The technical key points of this model:

1. The two centers use separate IP address segments, and both publish routes to the outside world.

two。 DNS is used to direct client traffic to the corresponding data center.

Data Center switching:

1. Normally, two data centers provide services at the same time

two。 When a data center fails on one side, the service of the data center can be stopped by changing the DNS parsing.

Dual active data center benefits:

1. The two data centers are completely independent and do not interfere with each other.

two。 Less traffic between data centers

3. There is no need to consider the problem of firewall asynchronous routing

4. The link is used more efficiently and the economy is maximized.

Disadvantages of dual active data center:

On the technical side, I have not thought of the shortcomings for the time being. Feasibility, the transition from the existing dual-center to dual-live data center, in addition to IP address transformation, but also involves the application of DNS transformation, involving inter-departmental cooperation, driving difficulties, this model is more suitable for the new data center.

To select the data center network model, you need to investigate the deployment requirements of business / application / system / server, and consider it from top to bottom.

Note: whether it is active or dual-active, it is not difficult to achieve all kinds of "active" at the network level. In the production environment, the biggest bottleneck we are facing is actually the "double-active" problem of dual-center database.

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