Webmasters often face a dilemma: on the one hand, they desire search engines like Baidu and Google to crawl their website content to increase visibility; on the other hand, they are averse to web crawlers from unknown sources. This is why the concepts of "good crawlers" and "bad crawlers" have emerged.
When discussing "good crawlers," we have to discuss the Robots protocol, the access authorization agreement between web crawlers and web pages.
Definition of the Robots Protocol
The Robots Protocol (also known as the crawler protocol or robot protocol) stands for the "Robots Exclusion Protocol." It allows websites to instruct search engines which pages they can and cannot crawl.
Webmasters can create a text file named robots.txt in the root directory of their domain name. This file defines the pages that web crawlers can or cannot access, typically using regular expressions. Before crawling website content, crawlers first retrieve and parse this file, collecting data according to the rules contained in it. It's important to note that this protocol isn't mandatory; compliance depends primarily on the crawler's willingness to comply.
Web pages are connected by hyperlinks, forming a web structure. A crawler works like a spider roaming the web, with the following basic process:
A set of URLs are provided as seeds.
The crawler fetches these seeds, parses the HTML pages, and extracts hyperlinks.
The crawler continues to crawl pages linked by newly discovered links.
This process is cyclical. Therefore, webmasters have the following needs:
Protect certain pages containing personal privacy or website management information from being crawled, such as content that should not be made public.
Prevent specific search engines from crawling, such as Taobao's previous request that Baidu not crawl its content.
Small websites with limited traffic may prefer a more moderate crawling strategy.
Some dynamically generated pages may want to be indexed even without direct links.
The Robots Protocol was created to allow webmasters to communicate with crawlers and express their wishes.
How to Write the Robots Protocol
Before crawlers crawl a website, they first read the robots.txt file, so it must follow certain syntax rules. A basic robots.txt file contains two rules:
User-agent: Specifies which crawlers are subject to this rule.
Disallow: Lists URLs to block.
For example, crawlers declare their identity (User-agent) when crawling. You can consult the official documentation of relevant search engines to obtain the User-agent of different crawlers. Here are some examples of robots.txt file formats:
Allow all crawlers access:
makefile Copy
12User-agent: *
3Disallow:
45
Disallow all crawlers access:
makefile Copy
1User-agent: *
2Disallow: /
3
Disallow crawlers access to a specific directory:
javascript Copy
1User-agent: *
2Disallow: /a/3Disallow: /b/45
Advanced Robots Protocol Knowledge
1. Sitemap
Crawlers primarily discover new web pages through links, but how can search engines be informed of the existence of pages without links pointing to them? This is where sitemaps come in. The simplest form of a sitemap is an XML file that lists a website's URLs and related data. Webmasters typically place the location of the sitemap in robots.txt to make it easier for crawlers to find it.
2. Meta Tags
While robots.txt is used to control whether search engines can crawl certain content, some web pages may still be indexed by search engines. In these cases, meta tags can be used for more granular control. For example, using
Copy
1<meta name="robots" content="noindex" >
can prevent specific web pages from being indexed.
3. Crawl-delay
In addition to controlling which pages are crawled, robots.txt can also set the crawler's crawling frequency. For example,
Copy
1crawl-delay: 5
specifies a five-second wait between crawls. However, Google no longer supports this feature.
Challenges and Solutions to the Robots Protocol
While the Robots protocol provides webmasters with tools to communicate with web crawlers, its practical application still presents numerous challenges. The following are some of the main challenges and their solutions:
1. Protocol Compliance Issues
Not all crawlers adhere to the Robots protocol. Malicious crawlers often ignore this protocol and may crawl a large portion of your website's content, leading to data leakage or bandwidth usage.
Countermeasures:
Technical Measures: Website administrators should implement additional security measures, such as user authentication, IP address blocking, and rate limiting, to prevent unauthorized access.
Monitoring and Alerts: Implement a monitoring system to track access logs in real time, promptly detecting and blocking abnormal traffic.
2. Cache Update Delays
Crawlers often cache robots.txt files. This means that even if a website administrator updates the rules, crawlers may continue to follow the old rules for a period of time, rendering the management ineffective.
Countermeasures:
Use Webmaster Tools: Some search engines provide Webmaster Tools that allow website administrators to request a recrawl of the robots.txt file, accelerating the implementation of updates.
Regular Inspection and Updates: Administrators should regularly check website access to ensure that the rules in the robots.txt file reflect the latest management requirements.
3. Number of Malicious Crawlers
On the internet, malicious crawlers often outnumber compliant crawlers. These crawlers may perform data collection, competitor analysis, or even cause website crashes.
Countermeasures:
Use anti-crawler services: Consider using a professional anti-crawler solution, such as Qian'an Technology's WARDEN platform, with customized features to detect and block malicious crawlers.
Set access rate limits: Control access frequency to prevent a single user or crawler from overloading the server.
4. Information Leakage Risk
Even with the Robots protocol, some sensitive information may still be found by search engines through external links or indexing, leading to information leakage.
Countermeasures:
Use meta tags: Use the noindex meta tag on web pages to prevent sensitive content from being indexed by search engines.
Data Encryption and Hiding: Implement encrypted storage and access controls for important data to ensure that even if crawled, the actual content cannot be retrieved.
5. Insufficient Protocol Flexibility
The Robots protocol's rules are relatively simple and cannot meet the needs of all complex scenarios. For example, dynamically generated content or crawling restrictions during specific time periods may not be effectively managed using the standard robots.txt file.
Response Strategies:
Combining the Robots protocol with other technologies, such as API access control and time-limit policies, allows for more refined management.
Dynamic Strategy Adjustment: Flexibly adjust crawling strategies based on website traffic and data types to meet varying needs.
Conclusion
While the Robots protocol provides a basic management tool for webmasters, it alone is far from sufficient in the face of increasingly complex network environments and malicious activity. By combining multiple technologies and strategies, webmasters can more effectively protect website content and maintain data security.
