cors is not defined

This error message usually appears in the browser console when making an HTTP request to a different domain than the one from which the JavaScript code is served.

To solve this issue, you need to enable Cross-Origin Resource Sharing (CORS) on the server that you are sending the request to. This can be done by adding the appropriate headers to the server response.

If you don't have access to the server, you can use a proxy server to forward the request. Another option is to use JSONP instead of XMLHttpRequests, which allows making cross-domain requests by injecting a script tag into the page with a callback function.

相关问题

CORSMiddleware is not defined

`CORSMiddleware` is not a built-in module or function in Python. It is likely that you are trying to use this middleware in a web framework like Flask or Django, and you need to import it from the appropriate package.

For example, in Flask, you can import `CORS` from the `flask_cors` package and use it like this:

from flask import Flask
from flask_cors import CORS

app = Flask(__name__)
CORS(app)

In Django, you can import `CorsMiddleware` from the `corsheaders` package and add it to the `MIDDLEWARE` setting in your `settings.py` file:

MIDDLEWARE = [
    # ...
    'corsheaders.middleware.CorsMiddleware',
    # ...
]

Make sure you have installed the required packages before using them. You can do this by running `pip install <package-name>` in your command prompt or terminal.

tez ui页面访问为什么报 Adapter operation failed » Timeline server (ATS) is out of reach. Either it's down, or CORS is not enabled.

这个错误提示表示 Tez UI 无法访问 Timeline Server (ATS)，可能是因为 ATS 宕机或者未启用 CORS（跨域资源共享）。

要解决这个问题，可以尝试以下几个步骤：

1. 确认 ATS 是否正在运行，并且端口是否正确。

2. 检查 ATS 是否已启用跨域资源共享（CORS）。如果未启用，请在 ATS 配置文件中添加以下内容：

yarn.timeline-service.http-cross-origin.enabled=true
yarn.timeline-service.http-cross-origin.allowed-origins=*

3. 如果 Tez UI 和 ATS 不在同一台机器上，则需要在 ATS 的 Web 服务器上启用 CORS。例如，在 Apache 上，可以使用以下配置启用 CORS：

Header set Access-Control-Allow-Origin "*"

4. 如果 ATS 和 Tez UI 在同一台机器上，但是使用了不同的端口，则需要在 Tez UI 的 Web 服务器上启用代理。例如，在 Apache 上，可以使用以下配置启用代理：

ProxyPass /timeline http://localhost:<ATS端口>/timeline
ProxyPassReverse /timeline http://localhost:<ATS端口>/timeline

这些步骤中的任何一个都可能有助于解决 Adapter operation failed » Timeline server (ATS) is out of reach. Either it's down, or CORS is not enabled. 错误。