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Sample Envoy ratelimit 'hello world'

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Envoy Global rate limiting helloworld

Sample "hello world" application demonstrating basic aspects fo Envoy's Global Rate Limiting capability. This app configures a local envoy instance for an HTTP level rate limit filter and then uses Lyft's RateLimit Service as the backend.

Envoy's rate limit functions checks each request to see if it should go through or not either using a local instance specific criteria or globally. By local, the rate limit counter runs within the context of the single envoy proxy that handles the request. This means each proxy keeps track of the connections it manages and applies circuit braking. Global means there a single counter for all proxies will use as a basis for evaluating the request. Each proxy asks an upstream Rate Limiting Service (Lyfts, in this example) that would run outside of envoy for a decision on the request.

As this is just a tutorial, helloworld, we will use a single Envoy instance that talks to Lyft's Rate limiting gRPC service that also runs on the same machine. Realistically, you probably want set this up to run within a kubernetes cluster with envoy as a sidecar and the rate limiting service running by itself.

Please also review the following

note: I did not this this at scale and don't know how it impacts performance since each requests is checked.

Global rate limiting scheme

We're running a stock quote service at endpoint:

/quote: Get stock quote Users are authenticated using the standard HTTP_AUTHORIZATION (Authorization: Bearer token). The quote service has two levels of service: basic and enhanced where the service level is requested as a header value.

We would like to setup rate limit controls such that:

  1. Anonymous users (not auth token) are allowed 2 req/min of any service level
  2. Users with auth allowed upto 20 req/min of any service level
  3. Users with auth and "enhanced" service level allowed 10 req/min
  4. Users with auth and "basic" service level allowed 15 req/min

Which means a single authenticated user can make with in one minute

  • 15 basic + 5 enhanced
  • 10 basic + 10 enhanced

So how do we do this with envoy? Basically you define rules in the envoy filters that constructs a vector of key-value messages (called descriptors) to the external rate limiting service. This took me sometime to understand but you basically have carefully construct the data thats emitted from Envoy and match that with a configuration on the Rate Limiting Service.

To separate out the authorization limits form the actual rate control, we split the checks into envoy filter stages. The first split up the http handlers in envoy into two stages. The first stage just checks and limits the authorization header existence while the second stage does the actual policy checks we defined

Setup Rate Limiting Service

Lyft's service implementation uses redis so run:

docker run -p 6379:6379 redis

Then setup some env variables and run the service

export USE_STATSD=false 
export LOG_LEVEL=debug 
export REDIS_SOCKET_TYPE=tcp 
export REDIS_URL=localhost:6379 
export RUNTIME_ROOT=`pwd`/runtime_root/ 
export RUNTIME_SUBDIRECTORY=ratelimit


git clone https://github.com/lyft/ratelimit.git
cd ratelimit

# the following is done since Lyft glide-based install doens' support go modules in my version
# https://github.com/lyft/ratelimit/pull/101

rm go.mod
go run src/service_cmd/main.go

Once you run the service, you should see the configurations loaded:

DEBU[0000] loading domain: apis                         
DEBU[0000] loading descriptor: key=apis.header_match_quote-path-vip 
DEBU[0000] loading descriptor: key=apis.header_match_quote-path-vip.priority-level_enhanced ratelimit={requests_per_unit=15, unit=MINUTE} 
DEBU[0000] loading descriptor: key=apis.header_match_quote-path-vip.service-level_basic ratelimit={requests_per_unit=10, unit=MINUTE} 
DEBU[0000] loading descriptor: key=apis.header_match_quote-path-user-limit 
DEBU[0000] loading descriptor: key=apis.header_match_quote-path-user-limit.auth_token ratelimit={requests_per_unit=20, unit=MINUTE} 
DEBU[0000] loading descriptor: key=apis.header_match_quote-path-auth ratelimit={requests_per_unit=2, unit=MINUTE} 

Setup backend and Envoy

Download envoy binary here

The 'backend' for our quote service is just a fake upstream service (it really doens't matter since we're focusing on envoy and ratelimits). In our example here, we just use nginx as s the quote service. Run

docker run -p 11000:80 nginx

(as an aside, i tried to use direct_response as the backend but that did not honor rate limits)

Run Envoy

envoy -c bbc.yaml -l debug

At this point, the rate limiters should be working.

Testing

Lets go through the criteria we seutp earlier;

1. Anonymous access

For the stage0 anonymous users: we can achieve that by applying header_value_match RateLimit.Action that emits values if the Authorization header is not found (note the expect_match: false setting)

              rate_limits:
              - actions:                                 
                - header_value_match:
                    descriptor_value: quote-path-auth
                    expect_match: false
                    headers:
                    - name: ":path"
                      exact_match: "/quote"
                    - name: "Authorization"                      
                stage: 0

THe corresponding Lyft configuration that handles the descriptor above is

- key: header_match
  value: quote-path-auth
  rate_limit:
    unit: minute
    requests_per_unit: 2

For reference, see

Which means a descriptor like ("header_match", "quote-path-auth") gets sent everytime the Authorization header isn't present an gets throttled at 2/min.

To test, in a new window run:

$ for i in {1..1000}; do curl -s -o /dev/null -w "$i->%{http_code} "  http://localhost:10000/quote; sleep 1; done
  1->200 2->200 **3->429 4->429 5->429**

In the window where you are running the rate limit service, you should see the request counters incremented with each request and eventually a report that this vector is over the limit:

DEBU[0110] looking up cache key: apis_header_match_quote-path-auth_1571615400 
DEBU[0110] cache key: apis_header_match_quote-path-auth_1571615400 current: 1 
DEBU[0111] cache key: apis_header_match_quote-path-auth_1571615400 current: 2 
DEBU[0112] cache key: apis_header_match_quote-path-auth_1571615400 current: 3 
..
DEBU[0120] [gostats] flushing counter ratelimit.service.rate_limit.apis.header_match_quote-path-auth.over_limit: 8

2. Authorized access without Service level

The second compounded limiter occurs if the Authorization: header is sent in and the counter the rate limiter uses is ofcourse not based on the simple existence of the header (which would be pretty useless) but a counter on every distinct value of that header. Which means "Authorization: Bearer Alice" has different counter than "Authorization: Bearer Bob". (ahd yes, this is a contrived example...a JWT based bearer token can be different for the same user and would get counted different... this is just for demonstration.)

The envoy configuration that emits the Authorization header value only when the /quote path is invoked is

              - actions:                                 
                - header_value_match:
                    descriptor_value: quote-path-user-limit
                    headers:
                    - name: ":path"
                      exact_match: "/quote"
                - request_headers:
                    header_name: "Authorization"
                    descriptor_key: auth_token                                    
                stage: 1  

Which is emitted as:

("header_match", "quote-path-user-limit").("auth_token", "__value_of_authorization_header__"))

Which matches the descriptor on the rate limiter:

- key: header_match
  value: quote-path-user-limit
  descriptors:
  - key: auth_token
    rate_limit:
      unit: minute
      requests_per_unit: 20

Each unique value for the authorization header is granted its own counter since the value itself isn't specified for the auth_token within the limiter.

Run the following and see the requests get denied after 20 or so counts:

$ for i in {1..1000}; do curl -s -H "Authorization: alice" -o /dev/null -w "$i->%{http_code} "  http://localhost:10000/quote; sleep 1; done 
   1->200 2->200 3->200 4->200 5->200 6->200 7->200 8->200 9->200 10->200 11->200 12->200 13->200 14->200 15->200 16->200 17->200 18->200 19->200 20->200 **21->429**

$ for i in {1..1000}; do curl -s -H "Authorization: bob" -o /dev/null -w "$i->%{http_code} "  http://localhost:10000/quote; sleep 1; done 
   1->200 2->200 3->200 4->200 5->200 6->200 7->200 8->200 9->200 10->200 11->200 12->200 13->200 14->200 15->200 16->200 17->200 18->200 19->200 20->200 **21->429**

Note the cache key counters includes a bit about the value (again, this is a contrived example; don't use the actual Authorization header value!!)

DEBU[0193] cache key: apis_header_match_quote-path-user-limit_auth_token_alice_1571618520 current: 1

DEBU[0430] cache key: apis_header_match_quote-path-user-limit_auth_token_bob_1571618760 current: 1

3. Authorized access with Service level

The third compound limiter further fine tunes the rate limiter using two header values: Authorization and the x-service-level enumberated value.

In the follwoing, we are emitting the x-service-level header as value for the /quote path. The Authorization header is emitted as well from the previous configuration. (TODO: find a way to collapse the rules...)

              - actions:
                - header_value_match:
                    descriptor_value: quote-path-vip
                    headers:
                    - name: ":path"
                      exact_match: "/quote"                                       
                - request_headers:
                    header_name: "x-service-level"
                    descriptor_key: service-level                    
                stage: 1

Ratelimit

- key: header_match
  value: quote-path-vip
  descriptors:
  - key: service-level
    value: "enhanced"  
    rate_limit:
      unit: minute
      requests_per_unit: 15
  - key: service-level
    value: "basic"  
    rate_limit:
      unit: minute
      requests_per_unit: 10

What the rules above state is if the client emits an authorized basic and enhanced requests, the rate limit will hit at 10 and 15 respectively within one minute window (per user as governed by the quote-path-user-limit rule)

$ for i in {1..1000}; do curl -s -H "Authorization: alice" -H "x-service-level: basic" -o /dev/null -w "$i->%{http_code} "  http://localhost:10000/quote; sleep 1; done 
  1->200 2->200 3->200 4->200 5->200 6->200 7->200 8->200 9->200 10->200 11->429

$ for i in {1..1000}; do curl -s -H "Authorization: alice" -H "x-service-level: enhanced" -o /dev/null -w "$i->%{http_code} "  http://localhost:10000/quote; sleep 1; done 
  1->200 2->200 3->200 4->200 5->200 6->200 7->200 8->200 9->200 10->200 11->200 12->200 13->200 14->200 15->200 16->429 17->429

Notice two counters are checked: one for the quote-path-user-limit and another for quote-path-vip. WHich ever one gets hit first will deny the request. In our exaple, the quote-path-vip was triggered first.

DEBU[0018] cache key: apis_header_match_quote-path-user-limit_auth_token_balice_1571619840 current: 1
DEBU[0018] cache key: apis_header_match_quote-path-vip_service-level_basic_1571619840 current: 11

DEBU[0343] cache key: apis_header_match_quote-path-user-limit_auth_token_alice_1571620140 current: 11 
DEBU[0343] cache key: apis_header_match_quote-path-vip_service-level_enhanced_1571620140 current: 11

To see it the other way, invoke a 'basic' request and cancel it once you see a deny

$  for i in {1..1000}; do curl -s -H "Authorization: bob" -H "x-service-level: basic" -o /dev/null -w "$i->%{http_code} "  http://localhost:10000/quote; sleep 1; done 
1->200 2->200 3->200 4->200 5->200 6->200 7->200 8->200 9->200 10->200 11->429 12->429 ^C

Then immediately call the 'enhanced' request.

$ for i in {1..1000}; do curl -s -H "Authorization: bob" -H "x-service-level: enhanced" -o /dev/null -w "$i->%{http_code} "  http://localhost:10000/quote; sleep 1; done 
  1->200 2->200 3->200 4->200 5->200 6->200 7->200 8->200 9->429 10->429 11->429 12->429 13->429 14->429 15->429 16->429 

Notice that the enhanced request failed on the 9th request or so (well before the 15 we configured). This is because the quote-path-user-limit was evaluated first and that caused the deny:

DEBU[0676] cache key: apis_header_match_quote-path-user-limit_auth_token_bob_1571620500 current: 20
DEBU[0676] cache key: apis_header_match_quote-path-vip_service-level_enhanced_1571620500 current: 9 

Notes:

  • Lyfts Rate limiter is pretty basic: its just a window based limit and lacks more advanced constructs like Token Bucket,etc. The docs do state they may add on more types as demand increases
  • The envoy rate limiting is pretty abstract..it was a bit difficult for me to understand even basic operations...there much i can improve here in this article the more learn. Please do feel free to suggest improvements if you figure out more advanced usage.

References

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Sample Envoy ratelimit 'hello world'