Debian Bullseye comes with Memcached 1.6.9. Things to consider before and during the upgrade:
* T258779 must be Resolved
* Reimage servers two at a time per DC, reimage next batch after reimaged servers reach a hit ratio of 0.85
** ensure that each gutter is picking up the traffic
**eqiad**
[] mc1037.eqiad.wmnet
[x] mc1038.eqiad.wmnet
[] mc1039.eqiad.wmnet
[x] mc1040.eqiad.wmnet
[] mc1041.eqiad.wmnet
[x] mc1042.eqiad.wmnet
[] mc1043.eqiad.wmnet
[x] mc1044.eqiad.wmnet
[] mc1045.eqiad.wmnet
[] mc1046.eqiad.wmnet
[] mc1047.eqiad.wmnet
[x] mc1048.eqiad.wmnet
[] mc1049.eqiad.wmnet
[] mc1050.eqiad.wmnet
[] mc1051.eqiad.wmnet
[] mc1052.eqiad.wmnet
[] mc1053.eqiad.wmnet
[] mc1054.eqiad.wmnet
[] mc-gp1001.eqiad.wmnet
[] mc-gp1002.eqiad.wmnet
[] mc-gp1003.eqiad.wmnet
**codfw**
[] mc2038.codfw.wmnet
[] mc2039.codfw.wmnet
[] mc2040.codfw.wmnet
[] mc2041.codfw.wmnet
[] mc2042.codfw.wmnet
[] mc2043.codfw.wmnet
[] mc2044.codfw.wmnet
[] mc2045.codfw.wmnet
[] mc2046.codfw.wmnet
[] mc2047.codfw.wmnet
[] mc2048.codfw.wmnet
[] mc2049.codfw.wmnet
[] mc2050.codfw.wmnet
[] mc2051.codfw.wmnet
[] mc2052.codfw.wmnet
[] mc2053.codfw.wmnet
[] mc2054.codfw.wmnet
[] mc2055.codfw.wmnet
[] mc-gp2001.codfw.wmnet
[] mc-gp2002.codfw.wmnet
[] mc-gp2003.codfw.wmnet