Example: Deploying a Multi-Tier Web Application

Multi-Tier Web Application Overview

A common requirement for a cloud tenant is to create a tiered web application in leased cloud space. The tenant enjoys the favorable economics of a private IT infrastructure within a shared services environment. The tenant seeks speedy setup and simplified operations.

The following example shows how to set up a simple tiered web application using Contrail. The example has a web server that a user accesses by means of a public floating IP address. The front-end web server gets the content it serves to customers from information stored in a SQL database server that resides on a back-end network. The web server can communicate directly with the database server without going through any gateways. The public (or client) can only communicate to the web server on the front-end network. The client is not allowed to communicate directly with any other parts of the infrastructure. See Figure 1.

Figure 1: Simple Tiered Web Use Case

Example: Setting Up Virtual Networks for a Simple Tiered Web Application

This example provides basic steps for setting up a simple multi-tier network application. Basic creation steps are provided, along with links to the full explanation for each of the creation steps. Refer to the links any time you need more information about completing a step.

Working with a system that has the Contrail software installed and provisioned, create a project named demo.
For more information; see Creating Projects in OpenStack for Configuring Tenants in Contrail.
In the demo project, create three virtual networks:
1. A network named public with IP address 10.84.41.0/24
  
  This is a special use virtual network for floating IP addresses— it is assigned an address block from the public floating address pool that is assigned to each web server. The assigned block is the only address block advertised outside of the data center to clients that want to reach the web services provided.
2. A network named frontend with IP address 192.168.1.0/24
  
  This network is the location where the web server virtual machine instances are launched and attached. The virtual machines are identified with private addresses that have been assigned to this virtual network.
3. A network named backend with IP address 192.168.2.0/24
  
  This network is the location where the database server virtual machines instances are launched and attached. The virtual machines are identified with private addresses that have been assigned to this virtual network.
For more information; see Creating a Virtual Network with OpenStack Contrail or Creating a Virtual Network with Juniper Networks Contrail.
Create a floating IP pool named public_pool for the public network within the demo project; see Figure 2.
Figure 2: Create Floating IP Pool
Allocate the floating IP pool public_pool to the demo project; see Figure 3.
Figure 3: Allocate Floating IP
Verify that the floating IP pool has been allocated; see Configure > Networking > Allocate Floating IPs.
Create a policy that allows any host to talk to any host using any IP address, protocol, and port, and apply this policy between the frontend network and the backend network.
This now allows communication between the web servers in the front-end network and the database servers in the back-end network.
Launch the virtual machine instances that represent the web server and the database server.
Note:
Your installation might not include the virtual machines needed for the web server and the database server. Contact your account team if you need to download the VMs for this setup.

On the Instances tab for this project, select Launch Instance and for each instance that you launch, complete the fields to make the following associations:
- Web server VM: select frontend network and the policy created to allow communication between frontend and backend networks. Apply the floating IP address pool to the web server.
- Database server VM: select backend network and the policy created to allow communication between frontend and backend networks.

Verifying the Multi-Tier Web Application

Verify your web setup.

To demonstrate this web application setup, go to the client machine, open a browser, and navigate to the address in the public network that is assigned to the web server in the frontend network.

The result will display the Contrail interface with various data populated, verifying that the web server is communicating with the database server in the backend network and retrieving data.

The client machine only has access to the public IP address. Attempts to browse to any of the addresses assigned to the frontend network or to the backend network should fail.

Sample Addressing Scheme for Simple Tiered Web Application

Use the information in Table 1 as a guide for addressing devices in the simple tiered web example.

Table 1: Sample Addressing Scheme for Example
System Name	Address Allocation
System001	10.84.11.100
System002	10.84.11.101
System003	10.84.11.102
System004	10.84.11.103
System005	10.84.11.104
MX80-1	10.84.11.253 10.84.45.1 (public connection)
MX80-2	10.84.11.252 10.84.45.2 (public connection)
EX4200	10.84.11.254 10.84.45.254 (public connection) 10.84.63.259 (public connection)
frontend network	192.168.1.0/24
backend network	192.168.2.0/24
public network (floating address)	10.84.41.0/24

Sample Physical Topology for Simple Tiered Web Application

Figure 4 provides a guideline diagram for the physical topology for the simple tiered web application example.

Figure 4: Sample Physical Topology for Simple Tiered Web Application

Sample Physical Topology Addressing

Figure 5 provides a guideline diagram for addressing the physical topology for the simple tiered web application example.

Figure 5: Sample Physical Topology Addressing

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