Chord sequence
A♭7 D♭7 A♭7 D♭7 A♭7 B♭m7 E♭7 A♭7 E♭7
In every key
Four-note rootless voicings in their two forms, with the 3rd or the 7th on the bottom, played over the root.
Heard in Ab major
All the chords
The basic blues with a ii-V in bars 9 and 10 in place of V-IV, and a V7 turnaround in the last bar.
Chords 6 to 7
Bbm7 Eb7
Over Ab7 · V7/IV
Mode 5 of Major
Over Db7 · IV7
Mode 4 of Melodic Minor
Over Ab7 · I7
Over Bbm7 · ii7
Mode 2 of Major
Over Eb7 · V7