The Agile Executive

Making Agile Work

Schedule Constraints in the Devops Triangle

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Last week’s post “The Devops Triangle” demonstrated the extension of Jim Highsmith‘s Agile Triangle to devops. The extension relied on adding compliance to the three traditional constraints of software development: scope, schedule, cost. A graphical representation of this extension is given in Figure 1.

Figure 1: Compliance as the Fourth Constraint in Devops Projects

This blog post examines how time/schedule should be governed in the devops context. It does so by building on the concluding observation in the previous post:

The Devops Triangle and the corresponding Tradeoff Matrix demonstrate how governance a la Agile can be extended to devops projects as far as compliance goes. The proposed governance framework however is incomplete in the following sense: schedule in devops projects can be a much more granular and stringent constraint than schedule in “dev only” projects.

For the schedule constraint in devops, I propose a schedule set.  It consists of  four components:

  • Lead Time or Engineering Time
  • Time to change
  • Time to deploy
  • Time to roll back

Lead Time/Engineering Time: These are customary metrics used in Kanban software development, as demonstrated in Figure 3.

Figure 3: The Engineering Time Metric Used by the BBC (David Joyce in the LSSC10 Conference)

Time to change: The amount of time it takes for the various stakeholders (e.g., dev, test, ops, customer support) to review the code to be deployed, approve its deployment and assign a time window for the deployment.

Time to deploy: The amount of time from (metaphorically speaking) pushing the Deploy “button” to completion of deployment.

Time to roll back: The amount of time to undo a deployment. (Rigorous that the engineering practices and IT processes might be, the time to roll back a deployment can’t be ignored – it is a critical risk parameter).

A graphical representation of these four schedule metrics together with the Devops Triangle is given in the figure below:

Figure 4: The Devops Triangle with a Schedule Set

Using hours as the common unit of measure, a typical schedule set could be {100, 48, 3, 2}. In this hypothetical example, it takes a little over 4 days to carry out the development of the code increment; 2 days to get approval for the change; 3 hours to deploy the code; and, 2 hours to roll back.

Whatever your specific schedule numbers might be, it is highly recommended you apply value stream mapping (see Figure 5 below) to your schedule set. Based on the findings of the value stream mapping, apply statistical process control methods like those illustrated in Figure 3 to continuously improving both the mean and the variances of the four schedule components.

Figure 5: An Example of Value Stream Mapping (Source: Wikipedia entry on the subject)

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