Flow Control

Flow control can be implemented via an independent API.

Log in to the CSS management console.
Choose Clusters in the navigation pane. On the Clusters page, locate the target cluster and click Access Kibana in the Operation column.

In the navigation pane on the left, choose Dev Tools and run the commands to query traffic control information.

Check the traffic control status of all nodes.
```
GET /_nodes/stats/filter
```
View the traffic control status of a specific node.
```
GET /_nodes/{nodeId}/stats/filter
```
{nodeId} indicates the ID of the node you want to check.

Example response:

{
  "_nodes" : {
    "total" : 1,
    "successful" : 1,
    "failed" : 0
  },
  "cluster_name" : "css-flowcontroller",
  "nodes" : {
    "ElBRNCMbTj6L1C-Wke-Dnw" : {
      "name" : "css-flowcontroller-ess-esn-1-1",
      "host" : "10.0.0.133",
      "timestamp" : 1613979513747,
      "flow_control" : {
        "transport" : {
          "concurrent_req" : 0,
          "rejected_concurrent" : 0,
          "rejected_new" : 0,
          "rejected_deny" : 0
        },
        "http" : {
          "concurrent_req" : 0,
          "rejected_concurrent" : 0,
          "rejected_new" : 0,
          "rejected_deny" : 0
        },
        "memory" : {
          "memory_allow" : 41,
          "memory_rejected" : 0
        },
        "cpu": {
          "rejected_cpu" : 0
        }
        "ip_address" : [
          {
            "ip" : "/10.0.0.198",
            "count" : 453
          },
          {
            "ip" : "/198.19.49.1",
            "count" : 42
          }
        ],
        "url_sample" : [
          {
            "url" : "/*/_search?pretty=true",
            "method" : "GET",
            "remote_address" : "/10.0.0.198:16763",
            "count" : 1
          }
        ]
      }
  }
}

In the response, the information of each node is separated. The http field records the numbers of concurrent connections and new connections. The memory records memory flow control statistics. The ip_address field records the recent client IP addresses that are accessed most recently. The url_sample field records the recent URLs that are requested most frequently. The cpu field records CPU flow control statistics.

**Table 1** Response parameters
Parameter	Description
concurrent_req	Number of TCP connections of a node, which is recorded no matter whether flow control is enabled. This value is similar to the value of current_open of the GET /_nodes/stats/http API but is smaller, because whitelisted IP addresses and internal node IP addresses are not counted.
rejected_concurrent	Number of concurrent connections rejected during HTTP flow control. This value is not cleared when HTTP flow control is disabled.
rejected_new	Number of new connections rejected during HTTP flow control. This value is not cleared when HTTP flow control is disabled.
rejected_deny	Number of requests rejected based on the blacklist during HTTP flow control. This value is not cleared when HTTP flow control is disabled.
memory_allow	Number of allowed requests during memory flow control. This parameter takes effect when memory flow control is enabled, and its value is not cleared after memory flow control is disabled. The requests from the paths in the allow_path whitelist are not recorded. If allow_path is set to **, no requests are recorded.
memory_rejected	Number of rejected requests during memory flow control. This parameter takes effect when memory flow control is enabled, and its value is not cleared after memory flow control is disabled. The requests from the paths in the allow_path whitelist are not recorded. If allow_path is set to **, no requests are recorded.
rejected_cpu	Number of requests rejected when the CPU flow control threshold is exceeded. This parameter takes effect when CPU flow control is enabled, and its value is not cleared after CPU flow control is disabled.
ip_address	IP addresses and the number of requests. For details, see Table 2.
url_sample	Request path sampling. The number of URLs of a request are collected based on the configured time and sampling interval. For details, see Table 3.

**Table 2** ip_address
Parameter	Description
ip	Source IP address for accessing the node.
method	Number of access requests from an IP address.

**Table 3** url_sample
Parameter	Description
url	Request URL
method	Method corresponding to the request path
remote_address	Source IP address and port number of the request
count	How many times a path is sampled