                 ┌──────────┐
                 │ Internet │
                 └────┬─────┘
                      │
                 ┌────┴─────┐
                 │ Firewall │
                 └────┬─────┘
                  /   │   \
                 /    │    \
       ┌───────┐  ┌───┴───┐  ┌───────┐
       │ Web 1 │  │ Web 2 │  │ Web 3 │
       └───────┘  └───────┘  └───────┘

            +---------------+
            |  User signs   |
            |      up       |
            +-------+-------+
                    |
                    v
            +---------------+
            | Validate form |
            +-------+-------+
                    |
                    v
                   / \
                  /   \
                 / OK? \
                 \     /
                  \   /
                   \ /
            yes     |      no
       +------------+------------+
       |                         |
       v                         v
+-------------+          +---------------+
| Create user |          | Show errors   |
+------+------+          +-------+-------+
       |                         |
       v                         +----> back to form
+-------------+
| Send email  |
+-------------+
