Upstream blocks in Nginx - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an upstream block in nginx?

An upstream block defines a group of backend servers that nginx can proxy requests to. It helps distribute traffic among multiple servers.

beginner

How do you define multiple servers inside an upstream block?

Inside the upstream block, list each server with the server directive, for example:

upstream backend {
  server 192.168.1.10;
  server 192.168.1.11;
}

beginner

What is the purpose of the proxy_pass directive in relation to upstream blocks?

The proxy_pass directive tells nginx to forward client requests to the servers defined in an upstream block, enabling load balancing.

intermediate

Name two load balancing methods supported in nginx upstream blocks.

Two common methods are:
1. round-robin (default): requests are distributed evenly.
2. least_conn: requests go to the server with the fewest active connections.

intermediate

How can you mark a server as a backup in an upstream block?

Add the backup parameter to the server directive. This server will only receive traffic if all primary servers are down.

server 192.168.1.12 backup;

What does an upstream block in nginx do?

A Configures SSL certificates

B Sets client request timeout

C Defines backend servers for load balancing

D Specifies static file locations

An upstream block groups backend servers to distribute client requests.

Which directive inside an upstream block lists backend servers?

A proxy_pass

B server

C location

D listen

The server directive defines each backend server inside the upstream block.

What is the default load balancing method in nginx upstream blocks?

A round-robin

B ip_hash

C random

D least_conn

The default method is round-robin, which distributes requests evenly.

How do you tell nginx to use an upstream block in a server configuration?

A Using <code>proxy_pass</code> with the upstream name

B Using <code>listen</code> directive

C Using <code>root</code> directive

D Using <code>error_page</code>

The proxy_pass directive forwards requests to the named upstream group.

What does the backup parameter do in an upstream server directive?

A Marks the server as primary

B Enables SSL on the server

C Disables the server

D Marks the server as a fallback used only if others fail

The backup server is used only when all primary servers are unavailable.

Explain how nginx uses an upstream block to balance load between servers.

Think about how nginx forwards requests to several servers.

Describe how to configure a backup server in an nginx upstream block and why it is useful.

Consider what happens if main servers go down.

Practice

1. What is the main purpose of an upstream block in an nginx configuration?

easy

A. To set caching rules for static files

B. To group backend servers for load balancing

C. To define client request headers

D. To configure SSL certificates

Solution

1. Step 1: Understand the role of upstream blocks

   Upstream blocks in nginx are used to group backend servers together.

2. Step 2: Identify the purpose of grouping

   This grouping allows nginx to distribute incoming traffic among these servers, which is called load balancing.

3. Final Answer:

   To group backend servers for load balancing -> Option B

4. Quick Check:

   Upstream blocks = backend server groups [OK]

Hint: Upstream blocks group servers for load balancing [OK]

Common Mistakes:

• Confusing upstream with SSL or caching settings
• Thinking upstream defines client headers
• Assuming upstream is for static file rules

2. Which of the following is the correct syntax to define an upstream block named backend with two servers server1.example.com and server2.example.com?

easy

A. upstream backend { server server1.example.com; server server2.example.com; }

B. upstream backend { server1.example.com; server2.example.com; }

C. upstream backend { backend server1.example.com; backend server2.example.com; }

D. upstream backend { server: server1.example.com; server: server2.example.com; }

Solution

1. Step 1: Recall the upstream block syntax

   The correct syntax requires the keyword server before each backend server address inside curly braces.

2. Step 2: Match the syntax with options

   upstream backend { server server1.example.com; server server2.example.com; } correctly uses server server1.example.com; and server server2.example.com; inside the upstream block.

3. Final Answer:

   upstream backend { server server1.example.com; server server2.example.com; } -> Option A

4. Quick Check:

   Each backend needs 'server' keyword [OK]

Hint: Each server line starts with 'server' keyword [OK]

Common Mistakes:

• Omitting 'server' keyword before addresses
• Using colons instead of spaces
• Adding extra keywords like 'backend' inside block

3. Given this nginx upstream block:

upstream backend {
    server 192.168.1.10 weight=3;
    server 192.168.1.11;
}

What does the weight=3 mean for 192.168.1.10?

medium

A. It receives three times more requests than 192.168.1.11

B. It is a backup server and only used if 192.168.1.11 fails

C. It limits connections to 3 simultaneous clients

D. It will be ignored because weight is invalid here

Solution

1. Step 1: Understand weight in upstream servers

   The weight parameter assigns relative load share to a server. A higher weight means more requests.

2. Step 2: Interpret the weight=3 for 192.168.1.10

   Since 192.168.1.10 has weight=3 and 192.168.1.11 has default weight=1, the first server gets 3 times more requests.

3. Final Answer:

   It receives three times more requests than 192.168.1.11 -> Option A

4. Quick Check:

   Weight controls request distribution [OK]

Hint: Weight multiplies request share for that server [OK]

Common Mistakes:

• Confusing weight with backup role
• Thinking weight limits connections
• Assuming weight is ignored if not 1

4. Identify the error in this upstream block configuration:

upstream backend {
    server 10.0.0.1;
    server 10.0.0.2 backup;
    server 10.0.0.3 weight=two;
}

medium

A. Upstream block cannot have more than two servers

B. Backup server must be listed first

C. Missing semicolon after server 10.0.0.1

D. The weight value 'two' is invalid; it must be a number

Solution

1. Step 1: Check syntax of weight parameter

   The weight parameter must be a numeric value. 'two' is a string and invalid.

2. Step 2: Verify other parts of the block

   Semicolons are present, backup server can be anywhere, and multiple servers are allowed.

3. Final Answer:

   The weight value 'two' is invalid; it must be a number -> Option D

4. Quick Check:

   Weight must be numeric [OK]

Hint: Weight values must be numbers, not words [OK]

Common Mistakes:

• Placing backup server only first
• Forgetting semicolons
• Limiting number of servers incorrectly

5. You want to configure an upstream block named app_servers with three servers: 10.1.1.1 (weight 5), 10.1.1.2 (weight 1), and 10.1.1.3 as a backup. Which configuration is correct?

hard

A. upstream app_servers { server 10.1.1.1 weight=5; server 10.1.1.2; server 10.1.1.3 backup=1; }

B. upstream app_servers { server 10.1.1.1 weight=5; server 10.1.1.2 weight=1 backup; server 10.1.1.3; }

C. upstream app_servers { server 10.1.1.1 weight=5; server 10.1.1.2 weight=1; server 10.1.1.3 backup; }

D. upstream app_servers { server 10.1.1.1; server 10.1.1.2 weight=1; server 10.1.1.3 backup weight=5; }

Solution

1. Step 1: Assign weights correctly

   Servers 10.1.1.1 and 10.1.1.2 must have weights 5 and 1 respectively, using weight=.

2. Step 2: Mark backup server properly

   Server 10.1.1.3 should be marked with the backup keyword without weight.

3. Step 3: Validate options

   upstream app_servers { server 10.1.1.1 weight=5; server 10.1.1.2 weight=1; server 10.1.1.3 backup; } correctly assigns weights and backup keyword. Others misuse backup or weight syntax.

4. Final Answer:

   upstream app_servers { server 10.1.1.1 weight=5; server 10.1.1.2 weight=1; server 10.1.1.3 backup; } -> Option C

5. Quick Check:

   Weight and backup keywords used correctly [OK]

Hint: Use 'weight=' for load, 'backup' alone for backup server [OK]

Common Mistakes:

• Using 'backup=1' instead of 'backup'
• Combining weight and backup on same server
• Omitting weight for weighted servers