Although crawling Internet data with web crawlers is fast, various problems are often encountered during the crawling process. This is because web crawlers will cause a load on the website server, and in serious cases, they will directly cause the website to crash, so most websites have taken certain countermeasures against crawlers. Generally speaking, there are several common problems when web crawlers crawl data:
1. Speed limit
Speed limit is a common way to fight crawlers. It works simply: the website forces users to perform a limited number of operations from a single IP address. The limit may vary from website to website and is based on the number of operations performed in a specific time period or the amount of data used by the user.
2. Captcha prompt
Captcha is another more complex way to limit web crawling. Users can trigger captchas by making too many requests in a short period of time, not properly covering the fingerprint of the web crawler, or using low-quality proxies.
3. Website structure changes
Websites are not static, especially when users crawl large websites. Sites often change HTML tags to disrupt users' web crawling scripts. For example, websites can delete or rename certain classes or element IDs, which will cause the user's parser to stop working.
4. The website uses JavaScript to run
Nowadays, many websites require users to click on certain areas to run JavaScript code in order to use them normally. For crawlers, conventional extraction tools do not have the function of processing dynamic pages, so they will encounter greater obstacles when crawling such websites.
5. Slow loading speed
When a website receives a large number of requests in a short period of time, its loading speed may slow down and become unstable. When the website is unstable, the crawler will refresh faster, but this only makes things worse. The website will interrupt the crawler to ensure that the site does not crash.
6. IP is restricted
There are many factors that may cause the user's crawler IP to be restricted, such as the data center proxy IP used by the user being identified by the website, the user's crawler crawling speed is too fast and is blocked, etc. When encountering this problem, users can choose to use a dynamic crawler proxy so that they use a different IP address each time they visit, so as to ensure that the IP is not restricted and the crawler crawls efficiently.
It has provided services to many well-known Internet companies, helping to improve the crawling efficiency of crawlers, supporting API batch use, and supporting multi-threaded high concurrency.