nginx_lua案例分析：动态路由实现

    这里的路由指的是在web开发中，访问路径以及具体实现内容的映射。比如，/a映射到某个具体的页面，这个就称之为一个路由。而动态路由，顾名思义就是动态添加这种路由映射关系。

    在nginx中，通过rewrite和proxy_pass来实现路由映射或者说反向代理，但是这种关系按照传统的配置必须写死在配置文件中，然后通过快速"无缝"重启nginx。虽说是无缝，但是其繁琐的配置和枯燥的重启操作还是无法避免。

    最近，在github上看到个项目ceryx，是nginx结合lua进行动态路由的映射的，也就是上面所说的映射关系，用lua来管理，虽然是比较简单的实现，但是可以分析学习下。该项目通过用redis的结构来保存这种映射关系，这样在nginx中可以快速获得这种关系，以便做出处理，同时，采用HTTP的形式暴露对redis这种路由关系进行管理的接口。

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from ceryx.db import RedisRouter


resource_fields = {
    'source': fields.String,
    'target': fields.String,
}

parser = reqparse.RequestParser()
parser.add_argument(
    'source', type=str, required=True, help='Source is required'
)
parser.add_argument(
    'target', type=str, required=True, help='Target is required'
)

router = RedisRouter.from_config()


def lookup_or_abort(source):
    """
    Returns the target for the given source, or aborts raising a 404
    """
    try:
        return {'source': source, 'target': router.lookup(source)}
    except RedisRouter.LookupNotFound:
        abort(
            404, message='Route with source {} doesn\'t exist'.format(source)
        )


class Route(Resource):
    """
    Resource describing a single Route. Supports GET, DELETE and PUT. The
    format is the following:
    ```
    {
        "source": "[source]",
        "target": "[target]"
    }
    ```
    """

    @marshal_with(resource_fields)
    def get(self, source):
        """
        Fetches the route with the given source
        """
        route = lookup_or_abort(source)
        return route

    @marshal_with(resource_fields)
    def delete(self, source):
        """
        Deletes the route with the given source
        """
        route = lookup_or_abort(source)
        router.delete(source)
        return route, 204

    @marshal_with(resource_fields)
    def put(self, source):
        """
        Creates or updates the route with the given source, pointing to the
        given target
        """
        args = parser.parse_args()
        router.insert(args['source'], args['target'])
        return args, 201

upstream fallback {
    server www.something.com;
}

server {
    listen 80;
    default_type text/html;

    location / {
        set $container_url "fallback";
        resolver 8.8.8.8;

        # Lua files
        access_by_lua_file lualib/router.lua;//切入点

        # Proxy configuration
        proxy_set_header Host $http_host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header  X-Real-IP  $remote_addr;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_redirect ~^(http://[^:]+):\d+(/.+)$ $2;
        proxy_redirect / /;

        # Upgrade headers
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";

        proxy_pass http://$container_url$request_uri;
    }
    ...
}

local container_url = ngx.var.container_url//拿到配置文件中的container_url
local host = ngx.var.host  //拿到请求的时候的host，比如我们请求http://www.xxx.com/a.html 那这里的host就是www.xxx.com

-- Check if key exists in local cache
local cache = ngx.shared.ceryx
local res, flags = cache:get(host)   //直接在nginx cache中拿host对应的路由映射，如果存在则直接返回结果
if res then
    ngx.var.container_url = res
    return
end

local redis = require "resty.redis"  // redis的连接代码  每次都会连接redis，
local red = redis:new()<span style="white-space:pre">			</span>//<span style="font-family: Arial, Helvetica, sans-serif;">这个操作比较相对比较耗时 所以接下来的操作才会在本地cache中存对应的关系</span>
red:set_timeout(100) -- 100 ms
local redis_host = os.getenv("CERYX_REDIS_HOST")
if not redis_host then redis_host = "127.0.0.1" end
local redis_port = os.getenv("CERYX_REDIS_PORT")
if not redis_port then redis_port = 6379 end
local res, err = red:connect(redis_host, redis_port)

-- Return if could not connect to Redis
if not res then
    return
end

-- Construct Redis key
local prefix = os.getenv("CERYX_REDIS_PREFIX")
if not prefix then prefix = "ceryx" end
local key = prefix .. ":routes:" .. host

-- Try to get target for host
res, err = red:get(key)
if not res or res == ngx.null then
    -- Construct Redis key for $wildcard
    key = prefix .. ":routes:$wildcard"
    res, err = red:get(key)
    if not res or res == ngx.null then
        return
    end
    ngx.var.container_url = res
    return
end

-- Save found key to local cache for 5 seconds
cache:set(host, res, 5)  // 在redis取出的映射关系存到redis的cache中避免下次继续连redis操作

ngx.var.container_url = res