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WebSocket Size Limit

Allows operators to specify a maximum size for incoming WebSocket messages.

Separate limits can be applied to clients and upstreams.

When an incoming message exceeds the limit:

  1. A close frame with status code 1009 is sent to the sender
  2. A close frame with status code 1001 is sent to the peer
  3. Both sides of the connection are closed

Configuration Reference

This plugin is compatible with DB-less mode.

In DB-less mode, you configure Kong Gateway declaratively. Therefore, the Admin API is mostly read-only. The only tasks it can perform are all related to handling the declarative config, including:

  • Setting a target's health status in the load balancer
  • Validating configurations against schemas
  • Uploading the declarative configuration using the /config endpoint

Example plugin configuration

The following examples provide some typical configurations for enabling the websocket-size-limit plugin on a service.

Make the following request:

curl -X POST http://localhost:8001/services/SERVICE_NAME|SERVICE_ID/plugins \
    --data "name=websocket-size-limit"  \
    --data 'config.client_max_payload=1024' \
    --data 'config.upstream_max_payload=16384'

Replace SERVICE_NAME|SERVICE_ID with the id or name of the service that this plugin configuration will target.

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: websocket-size-limit-example
config: 
  client_max_payload: '1024'
  upstream_max_payload: '16384'
plugin: websocket-size-limit

Next, apply the KongPlugin resource to a service by annotating the service as follows:

apiVersion: v1
kind: Service
metadata:
  name: SERVICE_NAME|SERVICE_ID
  labels:
    app: SERVICE_NAME|SERVICE_ID
  annotations:
    konghq.com/plugins: websocket-size-limit-example
spec:
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: SERVICE_NAME|SERVICE_ID
  selector:
    app: SERVICE_NAME|SERVICE_ID

Replace SERVICE_NAME|SERVICE_ID with the id or name of the service that this plugin configuration will target.

Note: The KongPlugin resource only needs to be defined once and can be applied to any service, consumer, or route in the namespace. If you want the plugin to be available cluster-wide, create the resource as a KongClusterPlugin instead of KongPlugin.

Add this section to your declarative configuration file:

plugins:
- name: websocket-size-limit
  service: SERVICE_NAME|SERVICE_ID
  config: 
    client_max_payload: '1024'
    upstream_max_payload: '16384'

Replace SERVICE_NAME|SERVICE_ID with the id or name of the service that this plugin configuration will target.

You can configure this plugin through the Konnect UI.

From the servicehub icon Service Hub, select a service version, then set up the plugin:

  1. In the Plugins section, click Add Plugin.
  2. Find and select the WebSocket Size Limit plugin.
  3. Click Create.

You can configure this plugin through the Kong Manager UI.

  1. In Kong Manager, select the workspace.
  2. From the Services section, click View for the service row.
  3. From the plugin section, click Add Plugin.
  4. Find and select the WebSocket Size Limit plugin.
    Note: If the plugin is greyed out, then it is not available for your product tier. See Kong Gateway tiers.
  5. If the option is available, select Scoped.
  6. Add the service name and ID to the Service field if it is not already pre-filled.
  7. Click Create.

The following examples provide some typical configurations for enabling the websocket-size-limit plugin on a route.

Make the following request:

curl -X POST http://localhost:8001/routes/ROUTE_NAME|ROUTE_ID/plugins \
  --data "name=websocket-size-limit"  \
    --data 'config.client_max_payload=1024' \
    --data 'config.upstream_max_payload=16384'

Replace ROUTE_NAME|ROUTE_ID with the id or name of the route that this plugin configuration will target.

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: websocket-size-limit-example
config: 
  client_max_payload: '1024'
  upstream_max_payload: '16384'
plugin: websocket-size-limit

Then, apply it to an ingress (route or routes) by annotating the ingress as follows:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: ROUTE_NAME|ROUTE_ID
  annotations:
    kubernetes.io/ingress.class: kong
    konghq.com/plugins: websocket-size-limit-example
spec:
  rules:
  - host: examplehostname.com
    http:
      paths:
      - path: /bar
        backend:
          service:
            name: echo
            port:
              number: 80

Replace ROUTE_NAME|ROUTE_ID with the id or name of the route that this plugin configuration will target.

Note: The KongPlugin resource only needs to be defined once and can be applied to any service, consumer, or route in the namespace. If you want the plugin to be available cluster-wide, create the resource as a KongClusterPlugin instead of KongPlugin.

Add this section to your declarative configuration file:

plugins:
- name: websocket-size-limit
  route: ROUTE_NAME
  config: 
    client_max_payload: '1024'
    upstream_max_payload: '16384'

Replace ROUTE_NAME|ROUTE_ID with the id or name of the route that this plugin configuration will target.

You can configure this plugin through the Konnect UI.

From the servicehub icon Service Hub, select a service version, then set up the plugin:

  1. Select a route.
  2. In the Plugins section, click Add Plugin.
  3. Find and select the WebSocket Size Limit plugin.
  4. Click Create.

You can configure this plugin through the Kong Manager UI.

  1. In Kong Manager, select the workspace.
  2. Open Routes from the menu, then click View for the route row.
  3. From the plugin section, click Add Plugin.
  4. Find and select the WebSocket Size Limit plugin.
    Note: If the plugin is greyed out, then it is not available for your product tier. See Kong Gateway tiers.
  5. If the option is available, select Scoped.
  6. Add the route ID if it is not already prefilled.
  7. Click Create.

A plugin which is not associated to any service, route, or consumer is considered global, and will be run on every request. Read the Plugin Reference and the Plugin Precedence sections for more information.

The following examples provide some typical configurations for enabling the websocket-size-limit plugin globally.

Make the following request:

curl -X POST http://localhost:8001/plugins/ \
  --data "name=websocket-size-limit"  \
    --data 'config.client_max_payload=1024' \
    --data 'config.upstream_max_payload=16384'

Create a KongClusterPlugin resource and label it as global:

apiVersion: configuration.konghq.com/v1
kind: KongClusterPlugin
metadata:
  name: <global-websocket-size-limit>
  annotations:
    kubernetes.io/ingress.class: kong
  labels:
    global: \"true\"
config: 
  client_max_payload: '1024'
  upstream_max_payload: '16384'
plugin: websocket-size-limit

Add a plugins entry in the declarative configuration file:

plugins:
- name: websocket-size-limit
  config: 
    client_max_payload: '1024'
    upstream_max_payload: '16384'

You can configure this plugin through the Kong Manager UI.

  1. In Kong Manager, select the workspace.
  2. Open Plugins from the menu, then click New Plugin.
  3. Find and select the WebSocket Size Limit plugin.
    Note: If the plugin is greyed out, then it is not available for your product tier. See Kong Gateway tiers.
  4. If the option is available, set the plugin scope to Global.
  5. Click Create.

Parameters

Here's a list of all the parameters which can be used in this plugin's configuration:

Form Parameter Description
name
required

Type: string		 The name of the plugin, in this case websocket-size-limit.
service.name or service.id

Type: string		 The name or ID of the service the plugin targets.

Set one of these parameters if adding the plugin to a service through the top-level /plugins endpoint.

Not required if using /services/SERVICE_NAME|SERVICE_ID/plugins.
route.name or route.id

Type: string		 The name or ID of the route the plugin targets.

Set one of these parameters if adding the plugin to a route through the top-level /plugins endpoint.

Not required if using /routes/ROUTE_NAME|ROUTE_ID/plugins.
enabled

Type: boolean

Default value: true		 Whether this plugin will be applied.
config.client_max_payload
semi-optional

Type: integer

Maximum size (in bytes) of client-originated WebSocket messages. Must be greater than 0 and less than 33554432 (32 MiB)
config.upstream_max_payload
semi-optional

Type: integer

Maximum size (in bytes) of upstream-originated WebSocket messages. Must be greater than 0 and less than 33554432 (32 MiB)

Usage

Limits can be applied to client messages, upstream messages, or both.

Limit client messages to 4 KiB

Use a request like this:

curl -i -X POST http://HOSTNAME:8001/services/SERVICE/plugins \
  --data "name=websocket-size-limit" \
  --data "config.client_max_payload=4096"

Add the following entry to the plugins: section in the declarative configuration file:

plugins:
- name: websocket-size-limit
  service: SERVICE
  config:
    client_max_payload: 4096

Limit upstream messages to 1 MiB

Use a request like this:

curl -i -X POST http://HOSTNAME:8001/services/SERVICE/plugins \
  --data "name=websocket-size-limit" \
  --data "config.upstream_max_payload=1048576"

Add the following entry to the plugins: section in the declarative configuration file:

plugins:
- name: websocket-size-limit
  service: SERVICE
  config:
    upstream_max_payload: 1048576

Limit both client and upstream messages

Use a request like this:

curl -i -X POST http://HOSTNAME:8001/services/SERVICE/plugins \
  --data "name=websocket-size-limit" \
  --data "config.client_max_payload=4096" \
  --data "config.upstream_max_payload=1048576"

Add the following entry to the plugins: section in the declarative configuration file:

plugins:
- name: websocket-size-limit
  service: SERVICE
  config:
    client_max_payload: 4096
    upstream_max_payload: 1048576

Raising the default limits

Kong Gateway applies the following default limits to incoming messages for all WebSocket services:

Sender Default Limit
client 1048576 (1MiB)
upstream 16777216 (16MiB)

This plugin can be used to increase the limit beyond the default. This example increases the client limit to 2 MiB, up from the default of 1 MiB:

Use a request like this:

curl -i -X POST http://HOSTNAME:8001/services/SERVICE/plugins \
  --data "name=websocket-size-limit" \
  --data "config.client_max_payload=2097152"

Add the following entry to the plugins: section in the declarative configuration file:

plugins:
- name: websocket-size-limit
  service: SERVICE
  config:
    client_max_payload: 2097152

The default client limit is smaller than the default upstream limit because proxying client-originated messages is much more computationally expensive than upstream messages. This is due to the client-to-server masking required by the WebSocket specification, so in general it is wise to maintain a lower limit for client messages.

How the plugin works

How limits are applied

Note: Limits are evaluated based on the message payload length and not the entire length of the WebSocket frame (header and payload).

Standalone data frames (text and binary)

For limits of 125 bytes or less, the message length is checked after reading and decoding the entire message into memory.

For limits of 125 bytes or more, the message length is checked from the frame header before the entire message is read from the socket buffer, allowing Kong Gateway to close the connection without having to read, and potentially unmask, the entire message into memory.

Continuation data frames

Kong Gateway aggregates continuation frames, buffering them in-memory before forwarding them to their final destination. In addition to evaluating limits on an individual frame basis, like singular text and binary frames, Kong Gateway also tracks the running size of all the frames that are buffered for aggregation. If an incoming continuation frame causes the total buffer size to exceed the limit, the message is rejected, and the connection is closed.

For example, assuming client_max_payload = 1024:

 .------.                                       .----.
 |Client|                                       |Kong|
 '------'                                       '----'
    |                                             |
    |     text(fin=false, len=500, msg=[...])     |
    |>------------------------------------------->| # buffer += 500 (500)
    |                                             |
    |                                             |
    |   continue(fin=false, len=500, msg=[...])   |
    |>------------------------------------------->| # buffer += 500 (1000)
    |                                             |
    |                                             |
    |   continue(fin=false, len=500, msg=[...])   |
    |>------------------------------------------->| # buffer += 500 (1500)
    |                                             | # buffer >= 1024 (limit exceeded!)
    |                                             |
    | close(status=1009, msg="Payload Too Large") |
    |<-------------------------------------------<|
 .------.                                       .----.
 |Client|                                       |Kong|
 '------'                                       '----'

For control frames

All control frames (ping, pong, and close) have a max payload size of 125 bytes, as per the WebSocket specification. Kong Gateway does not enforce any limits on control frames, even when they’re set to a value lower than 125.

See also