  Reliability of an application or solution in production environment is one of
the fundamental features where every SRE team is critically focused upon. At
the same time achieving extreme reliability comes with the cost which include
but not limited to slow pace of new feature deployments, operations cost and
opportunity cost. One such earlier effort in giving an objective metric to
strike the fine balance between acceptable reliability and product velocity is
error budget and its associated policy. There are also contemporary deployment
guidelines and controls per organization to ascertain the reliability of an
application deployment version into customer facing or production environments.
This work proposes new objective metrics called Application Deployment Score
estimated using dichotomous Item Response Theory model. This score is used to
assess the improvement trend of each application version deployed into customer
facing environment, identify the improvement scope for each application
deployment in each area of deployment guidelines and controls, adjust the error
budget i.e. soft error budget of a interdependent application in application
mesh by giving soft collective responsibility and finally defines a new metric
called deployment index which helps to assess the effectiveness of these
contemporary deployment guidelines and controls in upholding the agreed SLOs of
the application in customer facing environments. This study opens a new field
of research in developing new underlying latent indexes (i.e. new objective
metrics) in SRE and DevOps space.
