The Things Stack supports setting maximum limits for active resources. Access to each resource is limited by a unique identifier key, and it is possible to define resource limiting classes for fine-grained control.
Example configuration
The resource limiting configuration is split into multiple profiles. For each profile, we provide a name and the maximum number of concurrent resources allowed rate. The profile is associated with a number of resource limiting classes. Refer to the Limited Entities section below for a list of all available resource limiting classes and what they mean.
Enable resource limiting by adding the following configuration to your ttn-lw-stack.yml.
Resource limiting can be applied per application, as well as for all applications in a tenant. The values shown below are only meant as an example. Make sure to adjust them accordingly, depending on the actual traffic of your deployment.
resource-limiting:
profiles:
- name: Limit application data plane connections (MQTT and gRPC)
max-concurrent: 50
associations:
- as:conn
- name: Override limit for application `test-app-1` of tenant `test-tenant-1`
max-concurrent: 100
associations:
- as:conn:app:test-app-1@test-tenant-1
- name: Override limit for all applications of tenants `test-tenant-2` and `test-tenant-3`
max-concurrent: 200
associations:
- as:conn:tenant:test-tenant-2
- as:conn:tenant:test-tenant-3
Limited Entities
Application Server Data Plane Connections
| Description | Limit number of concurrent Application Server data plane connections by application and frontend. |
| Classes | as:conn:app:{{ AppUID }}</code> <code>as:conn:tenant:{{ TenantID }}</code> <code>as:conn:frontend:{{ Frontend }}</code> <code>as:conn |
| Key | as:conn:frontend:{{ Frontend }}:app:{{ AppUID }} |
| Example | as:conn:frontend:mqtt:app:app-1@tenant-1 |
For resources where multiple classes are defined, the first matching profile will be used. For example, if profile A is associated with class as:conn and profile B is associated with as:conn:app:my-application@my-tenant, then connections for my-application@my-tenant will use the limits from profile B.
Resource Limiting Actions
The following table describes how The Things Stack reacts when the maximum resource limits are exceeded.
| Resource | Resource Limit Action | Expected Client Action |
|---|---|---|
| gRPC Application Connections | Calls to Subscribe RPC will fail with an error of type ResourceExhausted. |
Terminate existing connections and retry. |
| MQTT Application Connections | A ServerUnavailable response is returned for new connections. |
Terminate existing connections and retry. |
For example, if an MQTT connection is failing due to resource limits exceeding, you will see an error such as Resource limit 16 exceeded for resource with key as:conn:frontend:mqtt:app:test-app-1@test-tenant-1. The resolution would be to terminate existing connections and retry.
External configuration
It is possible to load extra resource limiting profiles from an external file. Create a file named /opt/config/resource-limiting.yml (replace /opt/config with any path you like) with the following contents:
# If a profile is configured in `ttn-lw-stack.yml` for `as:conn`, then
# it will be overriden
profiles:
- name: Example profile
max-concurrent: 5
associations: [as:conn]
Then add the following config to ttn-lw-stack.yml (replace /opt/config with your path):
resource-limiting:
# This will read profiles from /opt/config/resource-limiting.yml
config-source: directory
directory: /opt/config