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Enforcing Operation Limits in the Apollo Router

Set constraints on depth, height, aliases, and root fields


This feature is only available with a GraphOS Enterprise plan.
You can test it out by signing up for a free Enterprise trial.

You can define operation limits in your 's configuration to reject potentially malicious requests. An that exceeds any specified limit is rejected (unless you run your router in warn_only mode).

Setup

To use operation limits, you must run v1.17 or later of the Apollo . Download the latest version.

You define operation limits in your router's YAML config file, like so:

router.yaml
limits:
max_depth: 100
max_height: 200
max_aliases: 30
max_root_fields: 20
# Uncomment to enable warn_only mode
# warn_only: true

Each limit takes an integer value. You can define any combination of supported limits.

Supported limits

max_depth

Limits the deepest nesting of selection sets in an operation, including in .

The GetBook operation below has depth three:

query GetBook {
book { # Depth 1 (root field)
...bookDetails
}
}
fragment bookDetails on Book {
details { # Depth 2 (nested under `book`)
... on ProductDetailsBook {
country # Depth 3 (nested under `details`)
}
}
}

max_height

Limits the number of unique fields included in an operation, including fields of fragments. If a particular field is included multiple times via , it's counted only once.

The GetUser operation below has height three:

query GetUser {
user { # 1
id # 2
name # 3
username: name # Aliased duplicate (not counted)
}
}

Each unique increments an operation's height by one, regardless of that field's return type (, object, or list).

max_aliases

Limits the total number of fields in an operation, including fields of fragments.

The GetUser operation below includes three aliases:

query GetUser {
user {
nickname: name # 1
username: name # 2
handle: name # 3
}
}

Each aliased field increments the alias count by one, regardless of that field's return type (scalar, object, or list).

max_root_fields

Limits the number of root fields in an operation, including root fields in fragments. If a particular root field is included multiple times via aliases, each usage is counted.

The following operation includes three root fields:

query GetTopProducts {
topBooks { # 1
id
}
topMovies { # 2
id
}
topGames { # 3
id
}
}

warn_only mode

If you run your router in warn_only mode, that exceed defined limits are not rejected. Instead, the router processes these operations as usual and emits a WARN trace that notes all exceeded limits, like so:

2023-03-15T19:08:23.123456Z WARN apollo_router::operation_limits: max_depth exceeded, max_depth: 3, current_op_depth: 5, operation: "query GetOwnerLocation {cat {owner {location {postalCode}}}}"

Running in warn_only mode can be useful while you're testing to determine the most appropriate limits to set for your .

You can enable or disable warn_only mode in your router's YAML config file, like so:

router.yaml
limits:
warn_only: true # warn_only mode always enabled

Response format for exceeded limits

Whenever your router rejects a request because it exceeds an operation limit, the router responds with a 400 HTTP status code and a standard error response body:

# HTTP 400
{
"data": {},
"errors": [
{
"message": "Maximum height (field count) limit exceeded in this operation",
"extensions": {
"code": "MAX_HEIGHT_LIMIT"
}
}
]
}

If you run your router in warn_only mode, the router logs the limit violation but executes the operation as normal, returning a 200 status code with the expected response.

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