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limit-conn
Apache APISIX
API Gateway
Limit Connection
This document contains information about the Apache APISIX limit-con Plugin, you can use it to limits the number of concurrent requests to your services.

Description

The limit-conn Plugin limits the number of concurrent requests to your services.

Attributes

Name Type Required Default Valid values Description
conn integer True conn > 0 Maximum number of concurrent requests allowed. Requests exceeding this ratio (and below conn + burst) will be delayed (configured by default_conn_delay).
burst integer True burst >= 0 Number of additional concurrent requests allowed to be delayed per second. If the number exceeds this hard limit, they will get rejected immediately.
default_conn_delay number True default_conn_delay > 0 Delay in seconds to process the concurrent requests exceeding conn (and conn + burst).
only_use_default_delay boolean False false [true,false] When set to true, the Plugin will always set a delay of default_conn_delay and would not use any other calculations.
key_type string False "var" ["var", "var_combination"] Type of user specified key to use.
key string True User specified key to base the request limiting on. If the key_type attribute is set to "var", the key will be treated as a name of variable, like remote_addr or consumer_name. If the key_type is set to "var_combination", the key will be a combination of variables, like $remote_addr $consumer_name. If the value of the key is empty, remote_addr will be set as the default key.
rejected_code string False 503 [200,...,599] HTTP status code returned when the requests exceeding the threshold are rejected.
rejected_msg string False non-empty Body of the response returned when the requests exceeding the threshold are rejected.
allow_degradation boolean False false When set to true enables Plugin degradation when the Plugin is temporarily unavailable and allows requests to continue.
policy string False "local" ["local", "redis", "redis-cluster"] Rate-limiting policies to use for retrieving and increment the limit count. When set to local the counters will be locally stored in memory on the node. When set to redis counters are stored on a Redis server and will be shared across the nodes. It is done usually for global speed limiting, and setting to redis-cluster uses a Redis cluster instead of a single instance.
redis_host string required when policy is redis Address of the Redis server. Used when the policy attribute is set to redis.
redis_port integer False 6379 [1,...] Port of the Redis server. Used when the policy attribute is set to redis.
redis_username string False Username for Redis authentication if Redis ACL is used (for Redis version >= 6.0). If you use the legacy authentication method requirepass to configure Redis password, configure only the redis_password. Used when the policy is set to redis.
redis_password string False Password for Redis authentication. Used when the policy is set to redis or redis-cluster.
redis_ssl boolean False false If set to true, then uses SSL to connect to redis instance. Used when the policy attribute is set to redis.
redis_ssl_verify boolean False false If set to true, then verifies the validity of the server SSL certificate. Used when the policy attribute is set to redis. See tcpsock:sslhandshake.
redis_database integer False 0 redis_database >= 0 Selected database of the Redis server (for single instance operation or when using Redis cloud with a single entrypoint). Used when the policy attribute is set to redis.
redis_timeout integer False 1000 [1,...] Timeout in milliseconds for any command submitted to the Redis server. Used when the policy attribute is set to redis or redis-cluster.
redis_cluster_nodes array required when policy is redis-cluster Addresses of Redis cluster nodes. Used when the policy attribute is set to redis-cluster.
redis_cluster_name string required when policy is redis-cluster Name of the Redis cluster service nodes. Used when the policy attribute is set to redis-cluster.
redis_cluster_ssl boolean False false If set to true, then uses SSL to connect to redis-cluster. Used when the policy attribute is set to redis-cluster.
redis_cluster_ssl_verify boolean False false If set to true, then verifies the validity of the server SSL certificate. Used when the policy attribute is set to redis-cluster.

Enable Plugin

You can enable the Plugin on a Route as shown below:

:::note You can fetch the admin_key from config.yaml and save to an environment variable with the following command:

admin_key=$(yq '.deployment.admin.admin_key[0].key' conf/config.yaml | sed 's/"//g')

:::

curl http://127.0.0.1:9180/apisix/admin/routes/1 \
-H "X-API-KEY: $admin_key" -X PUT -d '
{
    "methods": ["GET"],
    "uri": "/index.html",
    "plugins": {
        "limit-conn": {
            "conn": 1,
            "burst": 0,
            "default_conn_delay": 0.1,
            "rejected_code": 503,
            "key_type": "var",
            "key": "http_a"
        }
    },
    "upstream": {
        "type": "roundrobin",
        "nodes": {
            "127.0.0.1:1980": 1
        }
    }
}'

You can also configure the key_type to var_combination as shown:

curl http://127.0.0.1:9180/apisix/admin/routes/1 \
-H "X-API-KEY: $admin_key" -X PUT -d '
{
    "methods": ["GET"],
    "uri": "/index.html",
    "plugins": {
        "limit-conn": {
            "conn": 1,
            "burst": 0,
            "default_conn_delay": 0.1,
            "rejected_code": 503,
            "key_type": "var_combination",
            "key": "$consumer_name $remote_addr"
        }
    },
    "upstream": {
        "type": "roundrobin",
        "nodes": {
            "127.0.0.1:1980": 1
        }
    }
}'

Example usage

The example above configures the Plugin to only allow one connection on this route. When more than one request is received, the Plugin will respond with a 503 HTTP status code and reject the connection:

curl -i http://127.0.0.1:9080/index.html?sleep=20 &

curl -i http://127.0.0.1:9080/index.html?sleep=20
<html>
<head><title>503 Service Temporarily Unavailable</title></head>
<body>
<center><h1>503 Service Temporarily Unavailable</h1></center>
<hr><center>openresty</center>
</body>
</html>

Delete Plugin

To remove the limit-conn Plugin, you can delete the corresponding JSON configuration from the Plugin configuration. APISIX will automatically reload and you do not have to restart for this to take effect.

curl http://127.0.0.1:9180/apisix/admin/routes/1 \
-H "X-API-KEY: $admin_key" -X PUT -d '
{
    "methods": ["GET"],
    "uri": "/index.html",
    "id": 1,
    "plugins": {
    },
    "upstream": {
        "type": "roundrobin",
        "nodes": {
            "127.0.0.1:1980": 1
        }
    }
}'

Example of application scenarios

Limit the number of concurrent WebSocket connections

Apache APISIX supports WebSocket proxy, we can use limit-conn plugin to limit the number of concurrent WebSocket connections.

  1. Create a Route, enable the WebSocket proxy and the limit-conn plugin.

    curl http://127.0.0.1:9180/apisix/admin/routes/1 \
-H "X-API-KEY: $admin_key" -X PUT -d '
{
    "uri": "/ws",
    "enable_websocket": true,
    "plugins": {
        "limit-conn": {
            "conn": 1,
            "burst": 0,
            "default_conn_delay": 0.1,
            "rejected_code": 503,
            "key_type": "var",
            "key": "remote_addr"
        }
    },
    "upstream": {
        "type": "roundrobin",
        "nodes": {
            "127.0.0.1:1980": 1
        }
    }
}'

    The above route enables the WebSocket proxy on /ws, and limits the number of concurrent WebSocket connections to 1. More than 1 concurrent WebSocket connection will return 503 to reject the request.

  2. Initiate a WebSocket request, and the connection is established successfully.

    curl --include \
    --no-buffer \
    --header "Connection: Upgrade" \
    --header "Upgrade: websocket" \
    --header "Sec-WebSocket-Key: x3JJHMbDL1EzLkh9GBhXDw==" \
    --header "Sec-WebSocket-Version: 13" \
    --http1.1 \
    http://127.0.0.1:9080/ws
    HTTP/1.1 101 Switching Protocols

  3. Initiate the WebSocket request again in another terminal, the request will be rejected.

    HTTP/1.1 503 Service Temporarily Unavailable
···
<html>
<head><title>503 Service Temporarily Unavailable</title></head>
<body>
<center><h1>503 Service Temporarily Unavailable</h1></center>
<hr><center>openresty</center>
</body>
</html>