For the exam we will use the example of a bank ATM. The ATM supports multiple accounts and maintains a balance.

We will start with a super simple server. It will help everyone get comfortable compiling (and running) code.

It will also show the idea of a server loop, messages and a receive block.

This super-simple ATM will support the following actions. An account is created by depositing money to it.

atm:start() -> started
atm:check_balance(AccountNumber) -> {balance, Amount} | no_such_account | atm_closed
atm:withdraw(AccountNumber, Amount) -> {new_balance, Amount} | overdrawn | no_such_account | atm_closed
atm:deposit(AccountNumber, Amount) -> {new_balance, Amount} | atm_closed
atm:stop() -> stopped | atm_closed

To create an account, deposit money to it. To start we won't bother with PIN numbers.

• Bring up multiple Erlang nodes (node1, node2,...). Connect them with net_adm:ping.
• Bring an ATM up on each node.
• Deposit money to account 10000 on node1.
• Check account balances on various nodes and ensure they all agree.
• Withdraw money from account 10000 on node2.
• Check account balances on various nodes, and ensure they all agree.
• Add a new node to the cluster.
• Check account balances from new node and ensure they are correct.
• Disconnect node1 from the cluster.
• Deposit money to account 10000 on node1.
• Ensure the deposit is reflected on node1, but not on the other nodes.
• Deposit money to account 20000 on node2.
• Ensure the deposit is reflected on node2 and the other connected nodes, but not on node1.
• Rejoin node1 to the cluster.
• Ensure the balances for each node all jive.

Contribute your solution(s) by adding a folder named {your twitter handle}+{your erlang-vm language} such as:

/bryan_hunter+erlang/step2
/knewter+elixir/step1
/knewter+erlang/step1

Time to play!