Nexus Frame Works under 1 scrum master or many scrum master

What does the Nexus Guide say about this? Bear in mind that:

• the Nexus Guide does not contradict the Scrum Guide, and
• the roles, events, artifacts and rules of single team Scrum continue to apply.

I would caution about jumping in with a scaled framework with 5 teams. It's much easier to mature a single Scrum Team rather than start with 5 teams in a Nexus (or any other scaling framework) immediately. You may even find out that you don't need 5 teams to support the single product, and having fewer teams would reduce the complexity and overhead around synchronizing those teams.

If you are still planning on going forward with five teams in a Nexus, I'd point out a few things:

• Nothing in the Scrum Guide requires a 1-1 relationship between Scrum Masters and Scrum Teams. A single Scrum Master can be on multiple Scrum Teams.
• Nothing in the Nexus Guide requires each Scrum Team in the Nexus to have their own Scrum Master.
• In my experience, the number of Scrum Teams that a Scrum Master can support depends on the maturity of the Scrum Team as well as the experience and expertise of the Scrum Master. I would warn against having a single Scrum Master for 5 teams.
• Not all Scrum Masters are equal. Different Scrum Masters, with their different backgrounds and strengths, are able to solve different problems. Expecting 1 Scrum Master to effectively serve not only 5 Scrum Teams but also the organization may simply require a set of skills that is too broad for a single person to have.

Although there may be nothing in the rules of Scrum or Nexus that would stop the situation that you describe, it is not optimal. I would strongly suggest that an organization of 5 teams should have at least 2, if not 3, people with strong Scrum and agile coaching backgrounds. Depending on the maturity of the teams and organization, more may even be necessary. You'd be asking a lot of a single person.

Ok so we recently implemented Nexus back in Nov and have learned a ton of practical experience with this. I have a few questions for you:

• How large are your teams? Why 5 teams? Are they broken down by component area or are they more feature teams?
  • This is hugely important because your teams need to be right sized. They also should have a strong understanding of what they are working on. For instance, if each team will be component focused, you'll have to spend extra time planning and managing the dependencies between these teams. Example: Back End will have to finish their items before Front End can start.
• What is their experience using Scrum? 
  • If they are well versed and experienced using Scrum, your barrier to entry into Nexus will be far lower. If they are brand new, I strongly suggest against starting with Nexus. My coaches and trainers I know well (PST's - Blake McMillan & Don McGreal) always say "Nail it before you scale it". Scaling is hard! If you have no foundation, it will be a very painful journey. Just because you have multiple teams working on the same backlog, doesn't mean you HAVE to implement or use a scaled framework. 
• Who landed on Nexus as the preferred Framework?

As to your question: I would like to know does 1 scrum master works in nexus or multiple scrum master need to be placed.

Let me tell you, if you can make it so you've got a single SM per team; that'd be far better off. Within Nexus, you've got extra events that you have to account for as the SM. This is especially important on Review and Retro day. For us, we utilize the Nexus Integration Team a lot for Retros. Part 1, NIT meets to identify issues that impacted all teams. Part 2, Team Retros and the NIT brings input from Part 1 and engages the rest of the teams to get ideas for resolution (in addition to doing their normal team retros). Part 3, NIT gets back together and combines the ideas and figures out how to implement them. If you're the only SM, even if you have 2 teams, the timing is going to be crazy for you. To share some practicality, our Sprint Review is at 10-11:15. We have the remainder of the day to fit in all the retros. If you're the only SM, you either have to skip the part 2 retros for several teams and only go to 1 team, or find a way to spend a few minutes in each floating to and fro. That's nowhere close to ideal. There's not enough time in the day to stagger all of these unless you shorten the Retro to a time period that doesn't allow for true inspection and adaptation. In our group, I'm the SM for the NIT and 2 of our 3 Scrum Teams. So I've got it set so our schedule looks like this:

- 10 -11:15 Review

- 11:15 -12 Retro Part 1

- 12 -1 Lunch

- 1 - 2:30 Retro Part 2 Team A

- 2:30 - 4 Retro Part 2 Team B

- 4 - 5 Retro Part 3

It's a CRAZY LOOOONG DAY. Our 3rd team in the Nexus meets at 1 - 2:30 as well. Were I the only SM I'd have to skip retros or make them all shorter and I don't want to do that because then you get retros that are severely lacking in quality. 

All my rambling on to say, don't jump in the deep end with Nexus just because you have multiple teams working on the same backlog. Find a way to incorporate more SM's, 1:1 is best, 1:2 is Ok, 1:5 is bonkers and virtually impossible. Lastly, I'd love to help with any other questions related to Nexus, find me on LinkedIn and connect with me.

Thanks, Curtis for the great insight.