[Ethereum] Truffle – Migrate Contract to a private network in Azure

I try to migrate a Smart Contract to a private network running in Azure. It works fine with testrpc but when I try to migrate it to the (remote) private network I always get the following error:

Error: Invalid JSON RPC response: ""
    at Object.InvalidResponse (C:\Users\xxx\AppData\Roaming\npm\node_modules\truffle\node_modules\web3\lib\web3\errors.js:35:16)
    at XMLHttpRequest.request.onreadystatechange (C:\Users\xxx\AppData\Roaming\npm\node_modules\truffle\node_modules\web3\lib\web3\httpprovider.js:116:32)
    at XMLHttpRequestEventTarget.dispatchEvent (C:\Users\xxx\AppData\Roaming\npm\node_modules\truffle\node_modules\xhr2\lib\xhr2.js:64:18)
    at XMLHttpRequest._setReadyState (C:\Users\xxx\AppData\Roaming\npm\node_modules\truffle\node_modules\xhr2\lib\xhr2.js:354:12)
    at XMLHttpRequest._onHttpRequestError (C:\Users\xxx\AppData\Roaming\npm\node_modules\truffle\node_modules\xhr2\lib\xhr2.js:544:12)
    at ClientRequest.<anonymous> (C:\Users\xxx\AppData\Roaming\npm\node_modules\truffle\node_modules\xhr2\lib\xhr2.js:414:24)
    at emitOne (events.js:96:13)
    at ClientRequest.emit (events.js:188:7)
    at Socket.socketErrorListener (_http_client.js:310:9)
    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._tickDomainCallback (internal/process/next_tick.js:122:9)

What I did so far was creating and compiling the contract and modifying truffle.js to

module.exports = {
  networks: {
    azure: {
      network_id: xxx,
      host: "xxx.westeurope.cloudapp.azure.com",
      port: 8545   
    },
    development: {
      host: "localhost",
      port: 8545,
      network_id: "*" // Match any network id
    }
  }
};

When I run migrate --network azure in the truffle console the error occurs.

Does someone know how to do it correctly? Respectively why the error occurs?

Thanks