fix(medic#8205): Adds nginx resolver (medic#8206)

Adds `resolver` directive make nginx responsive to dynamic docker network IP allocation when containers are restarted. 

medic#8205

Author: dianabarsan

Diff for: nginx/templates/server.conf.template

@@ -1,5 +1,8 @@
+resolver 127.0.0.11 valid=10s; # 127.0.0.11 is from default /etc/resolv.conf
+set $upstream_endpoint http://${API_HOST}:${API_PORT};
+
 location / {
-  proxy_pass              http://${API_HOST}:${API_PORT};
+  proxy_pass              $upstream_endpoint;
   proxy_set_header        Host            $host;
   proxy_set_header        X-Real-IP       $remote_addr;
   proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;

Diff for: tests/integration/.mocharc.js

@@ -3,6 +3,7 @@ const chaiAsPromised = require('chai-as-promised');
 const chai = require('chai');
 chai.use(chaiExclude);
 chai.use(chaiAsPromised);
+global.expect = chai.expect;
 
 module.exports = {
   allowUncaught: false,

Diff for: tests/integration/api/server.spec.js

@@ -2,7 +2,6 @@ const utils = require('../../utils');
 const request = require('request');
 const constants = require('../../constants');
 const _ = require('lodash');
-const {expect} = require('chai');
 
 describe('server', () => {
   describe('JSON-only endpoints', () => {
@@ -181,4 +180,15 @@ describe('server', () => {
       expect(attachmentBody).to.equal(png);
     });
   });
+
+  describe('DNS resolver', () => {
+    it('nginx should resolve updated api ips', async () => {
+      await utils.stopHaproxy();
+      await utils.stopApi();
+      await utils.startHaproxy();
+      await utils.startApi();
+
+      await utils.request('/');
+    });
+  });
 });

Diff for: tests/utils.js

@@ -1245,6 +1245,8 @@ module.exports = {
     await startService('api');
     await listenForApi();
   },
+  stopHaproxy: () => stopService('haproxy'),
+  startHaproxy: () => startService('haproxy'),
 
   saveCredentials: (key, password) => {
     const options = {