Retrieve feature flags with API

The Evaluation Server offers two APIs that allow you to retrieve feature flags for both client-side and server-side sdks, specific to the desired environment.

The differences between client side and server side SDKs are:

Client side SDK is for single user but Server side SDK is for multiple users
Client side SDK relies on the Evaluation Server to evaluate all the flags while Server Side SDK evaluates the flags locally

ℹ️

Please note that you need to replace {Host} in the API requests with the appropriate host URL for your environment. {Host} can be the evaluation server host or the FeatBit Agent host, both of them provide the same API.

Polling With Timestamp Parameter

Both APIs support an optional timestamp query parameter that enables efficient polling for feature flag updates. When provided, the server will only return flags that have been modified after the specified timestamp. This helps reduce bandwidth and processing overhead by avoiding unnecessary data transfers when flags haven't changed.

How it works:

Make an initial request without the timestamp parameter to get all feature flags
Store the max timestamp value from the response
In subsequent polling requests, include the stored timestamp as a query parameter: ?timestamp={value}
The server will only return flags modified after that timestamp
Update your stored timestamp with the latest value from each response

Where to read the timestamp from:

Client-side requests: Extract the timestamp field from each feature flag object in the data.featureFlags array. Take the maximum value from all timestamps.
Server-side requests: Extract the updatedAt field from all objects in both the data.featureFlags and data.segments arrays. Find the latest among them and convert it to milliseconds.

Benefits:

Reduced network bandwidth usage
Lower server load
Faster response times when no changes have occurred

Client Side

For client-side requests, provide the client environment secret in the Authorization header.

Request

# Initial request (no timestamp)
curl -X POST {Host}/api/public/sdk/client/latest-all \
-H 'Content-Type: application/json' \
-H 'Authorization: client-env-secret' \
-d '{
    "keyId": "bot-id",
    "name": "bot",
    "customizedProperties": [
        {
            "name": "level",
            "value": "high"
        },
        {
            "name": "location",
            "value": "us"
        }
    ]
}'
 
# Subsequent polling request (with timestamp in milliseconds)
curl -X POST '{Host}/api/public/sdk/client/latest-all?timestamp=1712755780494' \
-H 'Content-Type: application/json' \
-H 'Authorization: client-env-secret' \
-d '{
    "keyId": "bot-id",
    "name": "bot",
    "customizedProperties": [
        {
            "name": "level",
            "value": "high"
        },
        {
            "name": "location",
            "value": "us"
        }
    ]
}'

Response

{
   "messageType":"data-sync",
   "data":{
      "eventType":"full",
      "userKeyId":"bot-id",
      "featureFlags":[
         {
            "id":"hello-world",
            "variation":"false",
            "variationType":"boolean",
            "variationId":"3f02a597-a150-4c3f-83b9-27a2de80c7dc",
            "matchReason":"flag disabled",
            "variationOptions":[
               {
                  "id":"fafb6319-9270-4a4b-b2c3-12d2be29e69a",
                  "value":"true"
               },
               {
                  "id":"3f02a597-a150-4c3f-83b9-27a2de80c7dc",
                  "value":"false"
               }
            ],
            "sendToExperiment":false,
            "timestamp":1712755780494
         }
      ]
   }
}

Server Side

For server-side requests, provide the server environment secret in the Authorization header.

Request

# Initial request (no timestamp)
curl -H "Authorization: server-env-secret" {Host}/api/public/sdk/server/latest-all
 
# Subsequent polling request (with timestamp in milliseconds)
curl -H "Authorization: server-env-secret" '{Host}/api/public/sdk/server/latest-all?timestamp=1712755780494'

Response

{
   "messageType":"data-sync",
   "data":{
      "eventType":"full",
      "featureFlags":[
         {
            "envId":"1331554d-98c4-41fe-ade4-68e6f5eeb54a",
            "name":"hello world",
            "key":"hello-world",
            "variationType":"boolean",
            "variations":[
               {
                  "id":"bbe8f444-090e-4a3b-99fa-b487bab424aa",
                  "value":"true"
               },
               {
                  "id":"cf8f9626-0d6f-4d05-a98f-8c3a50c85d0f",
                  "value":"false"
               }
            ],
            "targetUsers":[
               
            ],
            "rules":[
               
            ],
            "isEnabled":true,
            "disabledVariationId":"cf8f9626-0d6f-4d05-a98f-8c3a50c85d0f",
            "fallthrough":{
               "dispatchKey":null,
               "includedInExpt":true,
               "variations":[
                  {
                     "id":"bbe8f444-090e-4a3b-99fa-b487bab424aa",
                     "rollout":[
                        0,
                        1
                     ],
                     "exptRollout":1
                  }
               ]
            },
            "exptIncludeAllTargets":true,
            "tags":[
               
            ],
            "isArchived":false,
            "disabledVariation":{
               "id":"cf8f9626-0d6f-4d05-a98f-8c3a50c85d0f",
               "value":"false"
            },
            "creatorId":"b58fa8fd-eca2-460a-ab0f-e7758dbcec6a",
            "updatorId":"b58fa8fd-eca2-460a-ab0f-e7758dbcec6a",
            "createdAt":"2023-03-16T09:11:23.739Z",
            "updatedAt":"2023-03-16T09:11:26.0465535Z",
            "id":"4daca70f-86ae-4468-aee8-afc700977202"
         }
      ],
      "segments":[
         {
            "envId":"1331554d-98c4-41fe-ade4-68e6f5eeb54a",
            "name":"beta users",
            "description":"this is a segment for beta users",
            "included":[
               
            ],
            "excluded":[
               
            ],
            "rules":[
               
            ],
            "isArchived":false,
            "createdAt":"2023-03-16T09:18:21.1317917Z",
            "updatedAt":"2023-03-16T09:18:21.1317248Z",
            "id":"b2b91bbe-5d54-4d8a-882f-afc700995b23"
         }
      ]
   }
}

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