Properly rendering to framebuffer, that bigger than viewport

Hello. I have framebuffer, that bigger than viewport. When i’m trying to render into this framebuffer result is cut.
How properly apply shader to framebuffer that differ from viewport?

Set the viewport to match the framebuffer.

The first time that a context is bound to a drawable (window, pixmap, etc), the viewport is automatically set to the extent of the drawable. Thereafter, you need to set the viewport explicitly with glViewport.