Anthony Steele


It was the best of blue-green deployments, it was the worst of blue-green deployments

Let me tell a tale. I am talking about a previous employer, no name need be mentioned here.

We worked on an API that was in production, and it processed transactions over HTTP. It was part of a key process that made money for the company, so it should never be out of service. The load varied but it was never idle, there were always at least a few transactions per second, 24-7. Most transactions completed in under 2 seconds.

Meanwhile, development work on new features was ongoing, and updates due to new code happened about once a week. So how did this update happen without downtime?

The update process was simultaneously the best and the worst of Blue-Green deployment.

It was the best because it was gradual, zero-downtime, and checked, and had the ability to back out if any error was noticed.

It was the worst because of the sheer manual overhead and the resistance to automation, and the unaddressed impacts of that.

More people should embrace the best aspects of this deployment process, more people should shun the worst of it.

The good

There were at one point 16 servers, in 2 groups of 8 each. The groups were of course named “Blue” and “Green”. If a transaction failed outright with a HTTP 500 error, the upstream gateway would retry it up to 3 times. Load was usually evenly balanced between all servers, but this was configurable. Average load could be sustained by 1 group of 8 servers.

To deploy smoothly, all load was directed over to the green servers, then when blue was drained and idle, a deployment of a new build was done to the idle blue servers. Or vice versa. Thus we had deployment, without actual release to users yet.

Then tests were run on the new build on blue, and when passed, 1% of traffic was then sent to blue, and monitoring of logs and dashboards happened until we were happy with the outcome of this canary.

This process is relatively safe: consider the worst case; if the new deployment is “bad” and has some defect that somehow slipped through all testing, and it is throwing errors in common cases with real transactions. 1% of the load would go to the new code. This would occur once every 2 or 10 seconds, fail, and be retried with only a 1% chance of going to a blue server again on the second retry, and same again on the third retry. It’s possible to back out of a deployment before any transaction has the probability of more than an inconvenient retry delay to a few tens of transactions

If there were no errors, load was ramped up, with a pause for monitoring after each change, and if necessary, looking for specific transactions that have the characteristics to activate new code paths. A typical ramp up sequence was: 1%, 2%, 5%, 10%, 25%, 50%, and then if all is going well, complete it: 100% load on the new code on blue, a deploy to green, test on green and balance out again at 50-50 with the new version on both glue and green.

This is IMHO hard to improve on, as a gradual, testable, safe rollout of a live system with no downtime.

But it was also terrible.

The bad

Adding 1% traffic to blue meant an engineer entering “1” and “99” into 2 text-boxes in a well-known deploy tool, then clicking about 4 times to save, confirm, deploy, confirm. The total number of important keystrokes involved in a deployment was not small.

“Monitoring” was the people on the call with dashboards open and waiting a minute or several.

This was tedious and error prone and required keeping a lot of context in mind, with painstaking concentration. So the solution to that was to have more people on the call to check and confirm. Testing was manual too, so a Tester had to be on the call.

It typically took around 4 people more than 90 minutes to go through the whole thing.

The upshot is that releases couldn’t really happen more often than once a week on average - that is, some week there were 2 releases but it would slow down again afterwards when people stopped doing extraordinary effort. There just wasn’t capacity due to the manual test cycle, the multiple sign-offs, and scheduling and running the meeting. More often, and most of someone’s time would be spent on organizing and running releases.

It’s not just a “releasing was hard work” complaint that I have. It impacted the cycle time (The length of the feedback loop for code from Pull Request to production) a lot. This in turn made the delivery batches larger, which unless you push back hard, makes the cycle time larger again. So releases always rolled up about a week’s worth of work for a team, which also makes the release harder.

In terms of the 4 DORA metrics: Lead time for changes could not go down, Deployment frequency could not go up. Change failure rate in terms of changes that caused issues in production was negligible due to the diligent blue-green process, but deployments were occasionally backed out due to issues in one of a batch of changes.

Martin Fowler said: “If it hurts, do it more often. Frequency Reduces Difficulty.” Like a rusty wheel turning more easily when put back into use. This is due in part to smaller batch size and faster feedback. And in part due to “ironing out the kinks in your process”, i.e streamlining and automating process. But process does not always change so easily from the bottom up. As mentioned above, turning out releases more often through “extraordinary effort” - just working the process harder, was of limited use; it did not produce a sufficient change for long enough to demonstrate anything compelling.

It was around then that I started to say “These problems cannot be solved by adding process; the problems that can be solved by adding process have been thus solved; so the remaining problems are those caused by too much process.” I don’t think that this was ever even taken seriously. The impacts were either not understood or not deemed important. Process was process. Saying that it might not be useful was rocking the boat.

Despite the existence of automated unit tests, these were low-level and tightly coupled. The separate test team and their manual testing process going through each release was viewed as vital. It added a day or more to the release cycle. And they had no incentive to automate themselves out of their current job.

The fear of change given relatively infrequent and expensive releases was noticeable. Quality and incremental change was starved out in favour of hacking in new features that had a JIRA and a manager wanting them, as these were much easier to justify to the test team.

The thinking was of “why make deployments easier when you could be working on features?” or “Why fight against The Way We Do Things?”, “Why release more often than once a week, that would just be much more work doing releases?”.

The idea was that less human-in-the-loop processes must be “cowboy yeeting code” rather than “repeatable, consistent automation that removes human error and never takes short-cuts”. Asking to bypass management sign-off for each release could only be read as reckless corner-cutting, and not as a pre-requisite for quality. The incremental refactoring necessary for building quality in, never happened.

This is a big reason why I don’t work there any more.


I did direct people to online writing such as those from The DORA Institute to back up my suggestions, but did not get traction. I had a copy of the Accelerate book (Forsgren, Humble and Kim, 2018) but I could not bring myself to read it, as I felt that it would further elevate my stress levels when I knew that could not bring any of those desired practices into use. I was not the person who needed to read it.

Company culture matters. This is an example of the technical issues being easier to identify than the cultural issue, which they are actually downstream of. Cultural problems are often far harder to solve than the technical ones. You can’t get the time to fix a problem if it’s not even seen as a problem. You can’t get the time to fix a problem if you’re expected to only follow directions.

Identify issues all you like, but these things don’t change without support and buy-in from above. Is there psychological safety to make the suggestion, or will there merely be an immune response to expel the irritant?