Here is one approach.

Your notes C, D, Eb, F, G, Ab all belong to the key of C natural minor. Only note A don't fit into a key. Note A belongs to the key of C melodic minor, instead of Ab. So, using C minor (or it's relative major Eb) is a safe choice.

Diatonic triads in the key of C natural minor are

Cm - Ddim - Eb - Fm - Gm - Ab - Bb. Thus your chord progression would include chord functions ii°, iv, v, and VI

In the key of Eb major the functions would be ii, iii, IV and vii°

In that sence there isn't the the tonic chord at all, which makes me wonder is my logic completety wrong.