Estimate Memory / CPU / Disk needed

This page helps you estimate how much Memory / CPU / Disk the server you install The Littlest JupyterHub on should have. These are just guidelines to help with estimation - your actual needs will vary.

Memory

Memory is usually the biggest determinant of server size in most JupyterHub installations.

\[Server Memory Recommended = (Maximum concurrent users \times Maximum memory allowed per user) + 128MB\]

The 128MB is overhead for TLJH and related services. Server Memory Recommended is the amount of Memory (RAM) the server you acquire should have - we recommend erring on the side of ‘more Memory’. The other terms are explained below.

Maximum concurrent users

Even if your class has 100 students, most of them will not be using the JupyterHub actively at an given moment. At 2am on a normal night, maybe you’ll have 10 students using it. At 2am before a final, maybe you’ll have 60 students using it. Maybe you’ll have a lab session with all 100 of your students using it at the same time.

The maximum number of users actively using the JupyterHub at any given time determines how much memory your server will need. You’ll get better at estimating this number over time. We generally recommend between 40-60% of your total class size to start with.

Maximum memory allowed per user

Depending on what kinda work your users are doing, they will use different amounts of memory. The easiest way to determine this is to run through a typical user workflow yourself, and measure how much memory is used. You can use Check your memory usage to determine how much memory your user is using.

A good rule of thumb is to take the maximum amount of memory you used during your session, and add 20-40% headroom for users to ‘play around’. This is the maximum amount of memory that should be given to each user.

If users use more than this alloted amount of memory, their notebook kernel will restart.

CPU

CPU estimation is more forgiving than Memory estimation. If there isn’t enough CPU for your users, their computation becomes very slow - but does not stop, unlike with RAM.

\[Server CPU Recommended = (Maximum concurrent users \times Maximum CPU usage per user) + 0.2\]

The 0.2 is overhead for TLJH and related services. Server CPU Recommended is the amount of CPU the server you acquire should have. We recommend using the same process used to estimate Memory required for estimating CPU required.

Disk space

Unlike Memory & CPU, disk space is predicated on total number of users, rather than maximum concurrent users.

\[Server Disk Size Recommended = (Total \times Maximum disk usage per user) + 2GB\]

Resizing your server

Lots of cloud providers let your dynamically resize your server if you need it to be larger or smaller. Usually this requires a restart of the whole server - active users will be logged out, but otherwise usually nothing bad happens.