API versioning strategies in Express - Step-by-Step Execution

Concept Flow - API versioning strategies

Client sends request

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Check version info

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Match version strategy

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URL versioning

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Header versioning

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Query param versioning

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Accept header versioning

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Route to correct API handler

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Send response

The server checks the client's version info using different strategies, then routes the request to the matching API version handler.

Execution Sample

Express

const express = require('express');
const app = express();

app.get('/v1/users', (req, res) => res.send('Users v1'));
app.get('/v2/users', (req, res) => res.send('Users v2'));

app.listen(3000);

This code shows URL versioning by using different URL paths for API versions.

Execution Table

Step	Request URL	Version Detected	Routing Action	Response Sent
1	/v1/users	v1	Route to /v1/users handler	Users v1
2	/v2/users	v2	Route to /v2/users handler	Users v2
3	/users?version=1	No version in URL path	No match, 404 or fallback	Error or fallback response
4	/users	No version info	No match, 404 or fallback	Error or fallback response

💡 Requests without version info in URL path do not match any route and stop with error or fallback.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
Request URL		/v1/users	/v2/users	/users?version=1	/users
Version Detected	None	v1	v2	None	None
Routing Action	None	Route to /v1/users handler	Route to /v2/users handler	No match	No match
Response Sent	None	Users v1	Users v2	Error or fallback	Error or fallback

Key Moments - 2 Insights

Why does the request to '/users?version=1' not match any route in the example?

Because the example only defines versioning in the URL path (like '/v1/users'), not in query parameters. So '/users?version=1' does not match any defined route (see execution_table row 3).

How does the server know which version to use when using URL versioning?

It looks at the URL path prefix like '/v1/' or '/v2/' to detect the version and route accordingly (see execution_table rows 1 and 2).

Visual Quiz - 3 Questions

Look at the execution table, what response is sent when the request URL is '/v2/users'?

A Users v1

B Users v2

C Error or fallback response

D No response

💡 Hint

Check execution_table row 2 under 'Response Sent'

At which step does the version detection fail to find a version in the URL path?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at 'Version Detected' column in execution_table rows 3 and 4

If we add a header versioning strategy, how would the routing action change for '/users' with header 'API-Version: 1'?

A Route to /v1/users handler

B No match, 404 or fallback

C Route to /v2/users handler

D Route to default handler

💡 Hint

Header versioning uses headers to detect version, so routing can match even if URL path lacks version

Concept Snapshot

API versioning lets servers handle multiple API versions.
Common strategies:
- URL versioning: /v1/resource
- Header versioning: custom header like 'API-Version'
- Query param versioning: ?version=1
Server checks version info, routes to matching handler.
Helps keep old clients working while updating API.

Full Transcript

API versioning strategies help servers manage different versions of an API. The server checks the client's request for version information using methods like URL path prefixes, headers, or query parameters. Based on the detected version, the server routes the request to the correct version handler. For example, URL versioning uses paths like '/v1/users' or '/v2/users' to distinguish versions. If a request lacks version info or uses an unsupported method, the server may return an error or fallback response. This approach allows APIs to evolve without breaking existing clients.