I have just deployed my first droplet using MEAN one click installation. Droplet started off fine and connected with SSH. Now when I try to start the example app as given in the tutorial, it fails to start because it is unable to connect to mongodb.
Here is the error log:

+ Important warning: config.domain is empty. It should be set to the fully qualified domain of the app.
Could not connect to MongoDB!
{ MongoError: failed to connect to server [localhost:27017] on first connect
    at Pool.<anonymous> (/opt/mean/node_modules/mongoose/node_modules/mongodb-core/lib/topologies/server.js:313:35)
    at emitOne (events.js:96:13)
    at Pool.emit (events.js:188:7)
    at Connection.<anonymous> (/opt/mean/node_modules/mongoose/node_modules/mongodb-core/lib/connection/pool.js:271:12)
    at Connection.g (events.js:291:16)
    at emitTwo (events.js:106:13)
    at Connection.emit (events.js:191:7)
    at Socket.<anonymous> (/opt/mean/node_modules/mongoose/node_modules/mongodb-core/lib/connection/connection.js:165:49)
    at Socket.g (events.js:291:16)
    at emitOne (events.js:96:13)
    at Socket.emit (events.js:188:7)
    at emitErrorNT (net.js:1278:8)
    at _combinedTickCallback (internal/process/next_tick.js:74:11)
    at process._tickCallback (internal/process/next_tick.js:98:9)
  name: 'MongoError',
  message: 'failed to connect to server [localhost:27017] on first connect' }
/usr/bin/nodejs[3525]: ../src/debug-agent.cc:149:void node::debugger::Agent::Stop(): Assertion `(err) == (0)' failed.
 1: node::Abort() [node]
 2: node::Assert(char const* const (*) [4]) [node]
 3: 0x10c1bc2 [node]
 4: node::debugger::Agent::~Agent() [node]
 5: node::Start(int, char**) [node]
 6: __libc_start_main [/lib/x86_64-linux-gnu/libc.so.6]
 7: _start [node]
Aborted (core dumped)
[16:12:37] [nodemon] app crashed - waiting for file changes before starting...code

Isn’t MongoDB supposed to be installed out of the box? What am I missing here?