System comprising a cap for a medical fluid container and an attachment part, medical fluid container, and method for producing a fluid container

A system comprising:

• a cap for a medical fluid container;
• and
• an attachment part,
• the cap comprising at least a first port for providing a fluid connection between the fluid container and a device,
• the device being configured for withdrawing fluid from the fluid container and/or for supplying fluid into the fluid container,
• the first port comprising a first septum and a connection structure,
• the attachment part comprising a hollow spike and a joining structure in fluid communication with the hollow spike,
• the joining structure being configured to connect the device to the fluid container,
• the connection structure configured to be connected to a complementary connection structure of the attachment part in a releasable or non-releasable manner such that the hollow spike pierces the first septum,
• wherein the connection structure comprises a valve.