Backup servers in Nginx - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a backup server in the context of nginx?

A backup server is a secondary server that nginx uses only if the primary server is unavailable or fails. It helps keep the website or service running smoothly.

beginner

How do you define a backup server in an nginx upstream block?

You add the keyword backup after the server address inside the upstream block. For example:

upstream backend {
  server primary.example.com;
  server backup.example.com backup;
}

intermediate

Why use a backup server instead of just multiple primary servers?

A backup server is only used when all primary servers fail. This saves resources and avoids unnecessary load on the backup. It acts like a safety net.

intermediate

What happens if the primary server recovers after the backup server starts handling requests?

nginx automatically switches back to the primary server once it is healthy again, stopping requests to the backup server.

beginner

Write a simple nginx upstream block with one primary and one backup server.

upstream backend {
  server primary.example.com;
  server backup.example.com backup;
}

In nginx, what keyword marks a server as a backup in an upstream block?

A backup

B secondary

C failover

D reserve

The keyword backup is used to mark a server as a backup in nginx upstream configuration.

When does nginx send traffic to a backup server?

A All the time, in rotation

B Only when all primary servers are down

C Only during peak hours

D When the backup server is manually enabled

nginx uses the backup server only if all primary servers are unavailable.

What happens if the primary server comes back online after nginx switched to the backup?

A nginx continues using the backup server forever

B nginx requires a manual restart

C nginx switches back to the primary server automatically

D nginx sends traffic to both servers equally

nginx automatically switches back to the primary server once it is healthy again.

Which of these is NOT a benefit of using a backup server in nginx?

A Reduces load on primary servers during normal operation

B Acts as a safety net for failover

C Improves availability during primary server failure

D Ensures continuous service

Backup servers are idle during normal operation, so they do not reduce load on primary servers.

How do you test if your nginx backup server configuration works?

A Change the backup server to primary

B Restart nginx without changing config

C Add more primary servers

D Stop the primary server and check if requests go to the backup

Stopping the primary server simulates failure and tests if nginx routes traffic to the backup server.

Explain how nginx uses backup servers in load balancing and why they are important.

Think about what happens when the main server is down.

Describe how to configure a backup server in nginx and how nginx switches between primary and backup servers.

Focus on the nginx configuration syntax and behavior.

Practice

1. What is the main purpose of marking a server as backup in an upstream block in nginx?

easy

A. To use it only if all main servers are unavailable

B. To prioritize it over main servers for all requests

C. To permanently disable the server

D. To balance load equally with main servers

Solution

1. Step 1: Understand the role of backup servers

   Backup servers are fallback servers used only when main servers fail.

2. Step 2: Analyze the backup keyword effect

   Marking a server as backup means it will receive traffic only if main servers are down.

3. Final Answer:

   To use it only if all main servers are unavailable -> Option A

4. Quick Check:

   Backup servers = fallback only [OK]

Hint: Backup servers handle traffic only when main servers fail [OK]

Common Mistakes:

• Thinking backup servers share load equally
• Assuming backup servers are always active
• Confusing backup with disabled servers

2. Which of the following is the correct syntax to define a backup server in an nginx upstream block?

easy

A. server 192.168.1.10;

B. server backup 192.168.1.10;

C. server 192.168.1.10 backup;

D. backup server 192.168.1.10;

Solution

1. Step 1: Recall nginx upstream server syntax

   The correct syntax is server [IP] [parameters]; with parameters like backup after IP.

2. Step 2: Identify correct placement of backup

   The backup keyword comes after the IP address in the server line.

3. Final Answer:

   server 192.168.1.10 backup; -> Option C

4. Quick Check:

   Backup keyword after IP = correct syntax [OK]

Hint: Put 'backup' after IP in server line [OK]

Common Mistakes:

• Placing 'backup' before IP address
• Using 'backup server' instead of 'server ... backup;'
• Omitting semicolon at line end

3. Given this nginx upstream block:

upstream backend {
    server 10.0.0.1;
    server 10.0.0.2 backup;
}

Which server will nginx send requests to if 10.0.0.1 is up?

medium

A. 10.0.0.1 only

B. 10.0.0.2 only

C. Both 10.0.0.1 and 10.0.0.2 equally

D. No server, error occurs

Solution

1. Step 1: Understand upstream with backup server

   Main server 10.0.0.1 handles requests first; backup 10.0.0.2 is fallback.

2. Step 2: Check server availability

   Since 10.0.0.1 is up, nginx sends all requests there, ignoring backup.

3. Final Answer:

   10.0.0.1 only -> Option A

4. Quick Check:

   Backup used only if main down [OK]

Hint: Backup server used only if main server fails [OK]

Common Mistakes:

• Assuming backup server shares load
• Thinking backup server is always active
• Believing nginx sends requests to both simultaneously

4. You have this nginx upstream configuration:

upstream backend {
    server 192.168.0.1 backup;
    server 192.168.0.2;
}

What is wrong with this configuration?

medium

A. Backup keyword is misspelled

B. No semicolon after server lines

C. IP addresses are invalid

D. Nothing is wrong with this configuration

Solution

1. Step 1: Validate syntax and parameters

   All server lines have correct syntax, valid IPs, proper semicolons, and correct backup usage.

2. Step 2: Check server order

   Position of backup servers does not matter; nginx ignores them unless all main servers fail.

3. Final Answer:

   Nothing is wrong with this configuration -> Option D

4. Quick Check:

   Backup position irrelevant [OK]

Hint: Backup servers can be listed anywhere [OK]

Common Mistakes:

• Thinking backup servers must be listed after main servers
• Believing server order causes failures
• Assuming 192.168.x.x IPs are invalid

5. You want nginx to send traffic to server1 and server2 normally, but use backup1 and backup2 only if both main servers fail. Which configuration correctly sets this up?

hard

A. upstream backend {
server backup1;
server backup2;
server server1;
server server2;
}

B. upstream backend {
server server1;
server server2;
server backup1 backup;
server backup2 backup;
}

C. upstream backend {
server server1 backup;
server server2 backup;
server backup1;
server backup2;
}

D. upstream backend {
server server1;
server backup1;
server server2;
server backup2;
}

Solution

1. Step 1: Identify main and backup servers

   Main servers are server1 and server2; backup servers are backup1 and backup2.

2. Step 2: Apply correct syntax and order

   Main servers listed first without backup, backups listed after with backup keyword.

3. Step 3: Verify options

   upstream backend { server server1; server server2; server backup1 backup; server backup2 backup; } correctly lists main servers first, backups with backup keyword after.

4. Final Answer:

   upstream backend { server server1; server server2; server backup1 backup; server backup2 backup; } -> Option B

5. Quick Check:

   Main servers first, backups last with 'backup' keyword [OK]

Hint: List main servers first, backups last with 'backup' keyword [OK]

Common Mistakes:

• Placing backup servers before main servers
• Missing 'backup' keyword on backup servers
• Marking main servers as backup by mistake