Override config (#462)

* allowing override config to extend / replace elements in base

* fixing eslint

* adding env variable support for configuration

Author: Magesh Chandramouli

server/config/config.js

@@ -19,15 +19,24 @@
 
 const _ = require('lodash');
 const baseConfiguration = require('../config/base');
+const override = require('./override');
 
+let finalConfiguration =  _.merge({}, baseConfiguration);
+
+// if an override configuration file is provided, extend the base config with
+// the provided one. This is not a recursive merge, just a top level extend with
+// the overriden config
 if (process.env.HAYSTACK_OVERRIDES_CONFIG_PATH) {
   let overridesConfigration = process.env.HAYSTACK_OVERRIDES_CONFIG_PATH;
   if (!overridesConfigration.startsWith('/')) {
     overridesConfigration = `${process.cwd()}/${overridesConfigration}`;
   }
   // eslint-disable-next-line global-require, import/no-dynamic-require
   const environmentSpecificConfiguration = require(overridesConfigration);
-  module.exports = _.extend({}, baseConfiguration, environmentSpecificConfiguration);
-} else {
-  module.exports = baseConfiguration;
+  finalConfiguration = _.extend({}, finalConfiguration, environmentSpecificConfiguration);
 }
+
+// if there are environment variables, read them as objects and merge them
+// into the current configuration
+const overrideObject = override.readOverrides(process.env);
+module.exports = _.merge({}, finalConfiguration, overrideObject);

server/config/override.js

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2018 Expedia Group
+ *
+ *       Licensed under the Apache License, Version 2.0 (the License);
+ *       you may not use this file except in compliance with the License.
+ *       You may obtain a copy of the License at
+ *
+ *           http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *       Unless required by applicable law or agreed to in writing, software
+ *       distributed under the License is distributed on an AS IS BASIS,
+ *       WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *       See the License for the specific language governing permissions and
+ *       limitations under the License.
+ *
+ */
+
+const _ = require('lodash');
+
+const camelize = str => str.replace(/\W+(.)/g, (match, chr) => chr.toUpperCase());
+
+// this code will tokenize incoming keys to produce json objects
+// For example, a key like 'HAYSTACK_CONNECTORS_TRACES_ZIPKIN__URL'; with value 'foo'
+// will turn into '{ connectors: { traces: { zipkinUrl: 'foo' } } }'
+// Note:  a single _ splits the token into words and a __ combines them
+// to a camelCase
+module.exports = {
+
+  readOverrides: (collection) => {
+    const overrideData = {};
+    _.each(collection, (value, key) => {
+      if (key.startsWith('HAYSTACK_')) {
+        const parts = key.toLowerCase().replace(/__/g, ' ').split('_');
+        parts.shift();
+
+        let configObject = overrideData;
+        let part = parts.shift();
+        // console.log(`${key} [${parts}] ${value}`);
+
+        while (part) {
+          part = camelize(part);
+          if (parts.length) {
+            if (configObject[part] == null) {
+              configObject[part] = {};
+            }
+            configObject = configObject[part];
+          } else {
+            configObject[part] = value;
+          }
+          part = parts.shift();
+        }
+      }
+    });
+    return overrideData;
+  }
+};

test/server/config/override.spec.js

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2018 Expedia Group
+ *
+ *       Licensed under the Apache License, Version 2.0 (the License);
+ *       you may not use this file except in compliance with the License.
+ *       You may obtain a copy of the License at
+ *
+ *           http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *       Unless required by applicable law or agreed to in writing, software
+ *       distributed under the License is distributed on an AS IS BASIS,
+ *       WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *       See the License for the specific language governing permissions and
+ *       limitations under the License.
+ *
+ */
+
+const {expect} = require('chai');
+const override = require('../../../server/config/override');
+
+describe('override configuration reader', () => {
+  it('iterates over environment variables and returns an empty object if no matching variable is found', () => {
+    const envVariables = {
+      rvm_bin_path: '/Users/mchandramouli/.rvm/bin',
+      GEM_HOME: '/Users/mchandramouli/.rvm/gems/ruby-2.6.0',
+      NVM_CD_FLAGS: '',
+      TERM: 'xterm-256color'
+    };
+
+    const actual = override.readOverrides(envVariables);
+    expect(actual).to.deep.equal({});
+  });
+
+  it('iterates over environment variables and returns an object split by _', () => {
+    const envVariables = {
+      HAYSTACK_CONNECTORS_TRACES_ENABLED: 'true',
+      HAYSTACK_CONNECTORS_TRACES_PROVIDER: 'haystack',
+      TERM: 'xterm-256color'
+    };
+
+    const actual = override.readOverrides(envVariables);
+    expect(actual).to.deep.equal({
+                                   connectors: {
+                                     traces: {
+                                       enabled: 'true',
+                                       provider: 'haystack'
+                                     }
+                                   }
+                                 });
+  });
+
+  it('iterates over environment variables and returns an object split by _ and camelCase words split by __', () => {
+    const envVariables = {
+      HAYSTACK_CONNECTORS_TRENDS_CONNECTOR__NAME: 'haystack',
+      HAYSTACK_CONNECTORS_TRENDS_METRIC__TANK__URL: 'http://localhost:6000',
+      TERM: 'xterm-256color'
+    };
+
+    const actual = override.readOverrides(envVariables);
+    expect(actual).to.deep.equal({
+                                   connectors: {
+                                     trends: {
+                                       connectorName: 'haystack',
+                                       metricTankUrl: 'http://localhost:6000'
+                                     }
+                                   }
+                                 });
+  });
+});