This is the first of a two part series that offers guidelines on how to secure microservices accessible to clients through the public internet. This paper discusses the various security risks and countermeasures relating to microservices. There is always the possibility that security incidents will take place or that a particular security measure will not always be successful at preventing risks. This makes it imperative that a security architecture is in place which mitigates these risks. With the goal being to lower risks while allowing for other activities to take place, there is often a trade-off between practicality and security. The more places there are to attack, the easier it will be to find a weakness. The security architecture should reflect this in the form of countermeasures which respond to incidents. Different types of countermeasures work on varying attacks in different ways. Some make the attack more difficult while others make it clear what to do after the attack has already taken place. As this is where microservices play a critical role in enforcing security, there should be a comprehensive security plan which offers foresight into the possibility that the attacker might get past the initial layer of defense.