Classic way ...

• Add Curve Circle

• in Edit mode select two opposite controll points and move upward

• Convert to Mesh

• Extrude on Z axis and scale selection to zero on Z axis to flatten bottom ring

• add Solidify modifier

Classic way ...

• Add Cylinder 8 sides (octagon)

• in Edit mode select two opposite vertices and move upward 0.2 and in two in cross direction downward -0.2

• add Subsurf and Solidify modifier

Same can be done with Surface object > NURBS Cylinder