feat: allow stickiness on context-fields (#713)

* feat: allow stickiness on context-fields

* chore: docs for this feature

* fix: write a small e2e test

* fix: add stickiness to variants

docs/activation-strategies.md

@@ -35,6 +35,12 @@ A flexible rollout strategy which combines all gradual rollout strategies in to
 - **groupId** is used to ensure that different toggles will **hash differently** for the same user. The groupId defaults to _feature toggle name_, but the use can override it to _correlate rollout_ of multiple feature toggles.
 - **rollout** The percentage (0-100) you want to enable the feature toggle for.
 
+### Customize stickiness (beta)
+
+By enabling the stickiness option on a custom context field you can use it together with the flexible rollout strategy. This will guarantee a consistent behavior for specific values of this context field. PS! support for this feature currently being supported by the following SDKs:
+
+- [unleash-client-node](https://github.com/Unleash/unleash-client-node) (from v3.6.0)
+
 ## gradualRolloutUserId
 
 The `gradualRolloutUserId` strategy gradually activates a feature toggle for logged in users. Stickiness is based on the user ID. The strategy guarantees that the same user gets the same experience every time across devices. It also assures that a user which is among the first 10% will also be among the first 20% of the users. That way, we ensure the users get the same experience, even if we gradually increase the number of users exposed to a particular feature. To achieve this, we hash the user ID and normalize the hash value to a number between 1 and 100 with a simple modulo operator.

docs/feature-toggle-variants.md

@@ -19,7 +19,7 @@ If the toggle is considered **enabled**, the Unleash client will select the corr
 
 If the toggle is considered **disabled** you will get the built-in `disabled` variant.
 
-A json represntation of the empty variant will be the following:
+A json representation of the empty variant will be the following:
 
 ```json
 {
@@ -28,7 +28,7 @@ A json represntation of the empty variant will be the following:
 }
 ```
 
-The actual representation of the built-in the client SDK will vary slighty, to honor best pratices in various languages.
+The actual representation of the built-in the client SDK will vary slightly, to honor best practices in various languages.
 
 > If you change the number of variants, it will affect variant allocations. This means that some of the users will be moved to the next variant.
 

lib/db/context-field-store.js

@@ -9,6 +9,7 @@ const {
 const COLUMNS = [
     'name',
     'description',
+    'stickiness',
     'sort_order',
     'legal_values',
     'created_at',
@@ -18,6 +19,7 @@ const TABLE = 'context_fields';
 const mapRow = row => ({
     name: row.name,
     description: row.description,
+    stickiness: row.stickiness,
     sortOrder: row.sort_order,
     legalValues: row.legal_values ? row.legal_values.split(',') : undefined,
     createdAt: row.created_at,
@@ -63,6 +65,7 @@ class ContextFieldStore {
         return {
             name: data.name,
             description: data.description,
+            stickiness: data.stickiness,
             sort_order: data.sortOrder, // eslint-disable-line
             legal_values: data.legalValues ? data.legalValues.join(',') : null, // eslint-disable-line
             updated_at: data.createdAt, // eslint-disable-line

lib/routes/admin-api/context-schema.js

@@ -21,6 +21,10 @@ const contextSchema = joi
             .unique()
             .optional()
             .items(joi.string().max(100)),
+        stickiness: joi
+            .boolean()
+            .optional()
+            .default(false),
     })
     .options({ allowUnknown: false, stripUnknown: true });
 

lib/services/feature-schema.js

@@ -50,6 +50,7 @@ const variantsSchema = joi.object().keys({
             value: joi.string().required(),
         })
         .optional(),
+    stickiness: joi.string().default('default'),
     overrides: joi.array().items(
         joi
             .object()

lib/services/feature-schema.test.js

@@ -59,6 +59,7 @@ test('should allow weightType=fix', t => {
                 name: 'variant-a',
                 weight: 1,
                 weightType: 'fix',
+                stickiness: 'default',
             },
         ],
     };
@@ -103,6 +104,7 @@ test('should be possible to define variant overrides', t => {
                 name: 'variant-a',
                 weight: 1,
                 weightType: 'variable',
+                stickiness: 'default',
                 overrides: [
                     {
                         contextName: 'userId',

migrations/20210208203708-add-stickiness-to-context.js

@@ -0,0 +1,18 @@
+'use strict';
+
+exports.up = function(db, cb) {
+    db.runSql(
+        `
+        ALTER TABLE context_fields ADD COLUMN IF NOT EXISTS stickiness boolean DEFAULT false
+    `,
+        cb,
+    );
+};
+exports.down = function(db, cb) {
+    db.runSql(
+        `
+        ALTER TABLE context_fields DROP COLUMN IF EXISTS stickiness;
+    `,
+        cb,
+    );
+};

test/e2e/api/admin/context.e2e.test.js

@@ -82,6 +82,25 @@ test.serial('should update context field with legalValues', async t => {
         .expect(200);
 });
 
+test.serial('should create context field with stickiness', async t => {
+    t.plan(1);
+    const request = await setupApp(stores);
+    const name = 'with-sticky';
+    await request
+        .post('/api/admin/context')
+        .send({
+            name,
+            description: 'A context field supporting stickiness',
+            stickiness: true,
+        })
+        .set('Content-Type', 'application/json');
+
+    const res = await request.get(`/api/admin/context/${name}`);
+    const contextField = res.body;
+
+    t.is(contextField.stickiness, true);
+});
+
 test.serial('should not create context field when name is missing', async t => {
     t.plan(0);
     const request = await setupApp(stores);