This exam closes the "Operate and restore a stack" module of the Docker course, and with it the "Compose and operate an application" level. An application has lost its machine, and you must bring it back into service on another one, on your own, with no hints, using what the lessons of the module taught you. It teaches you nothing new, it checks what you have learned. Allow about 60 minutes on two virtual machines running Docker Engine 29.9.2 and Compose 5.6.1.
What you will learn
- Say what the exam provides, what it expects and what it grades you on.
- Spot the lessons to review before you start.
- Read your result to decide whether to move on to the next module or to consolidate.
Prerequisites
The lessons of the "Use Docker" level and those of the previous modules of the "Compose and operate an application" level must be finished. So must those of the "Operate and restore a stack" module: Read logs and attribute saturation, Back up and restore a Compose application and Update and roll back without losing data. The exam assumes that you know how to read the state of a stack, restore a backup and organize the networks of a composition.
Use the lab environment you used for the previous lessons. The service image and the backup are provided: the exam asks you to build nothing.
What does the exam ask of you?
The statement describes an application whose original machine can no longer be trusted. You must restart it on another one and leave it in a state the lab can check: it runs, it responds, it has found again the data it used to serve, and it has lost none of the protections of its architecture.
Nobody tells you what was destroyed. The statement gives the expected result, not the way to reach it. This page does not describe the scenario, so that the exam stays a measurement. You will read it in the lab statement, and only there.
How is it graded?
The lab does not look at the commands you typed. It reads back the state of the system at the moment you hand in your work: what is running, what responds, what the application serves and what the Docker engine has actually put in place. Two different ways of reaching the same state get the same grade.
Four checks of equal weight share the grade, and you must reach 75 points to pass. The grade is the number of checks passed divided by four, multiplied by a scale of 100 points minus the cost of the hints you asked for, rounded to the nearest integer (half to even in the case of an exact tie).
A critical requirement comes on top of the threshold: the witness record, written before the failure, must be served by the restored stack. Data that is present somewhere without being served does not count. If this check fails, the exam is refused whatever the total: a good total does not make up for lost data.
With no hint, three checks passed out of four give exactly 75 points and are enough, provided the critical requirement is met. Each hint lowers the maximum you can reach, and the first one already requires a perfect score:
| Hints requested | Cumulative cost | Scale | 4 out of 4 | 3 out of 4 | Verdict |
|---|---|---|---|---|---|
| None | 0 | 100 | 100 | 75 | 3 out of 4 are enough |
| The first | 10 | 90 | 90 | 68 (67.5 rounded) | 4 out of 4 required |
| The first two | 25 | 75 | 75 | 56 | 4 out of 4 required |
| The first three | 45 | 55 | 55 | 41 | Threshold not reachable |
| All four | 70 | 30 | 30 | 22 (22.5 rounded) | Threshold not reachable |
Which rules apply?
This exam measures, it does not guide you. Three rules follow from that.
- The lab offers four hints, from the vaguest to the most explicit, and each one costs you points, from 10 for the first to 25 for the last. From the first hint, you must pass all four checks; beyond two, the threshold is no longer reachable. An exam passed without a hint is therefore passed in full.
- You may consult the lessons of the course and the official Docker documentation, as you would at work.
- The statement explains nothing again, because the lessons of the module have already taught what you need to know.
If you are stuck, measure before you assume: ask the engine what really exists, on each machine, rather than deducing the state from what you think you have done.
Which lessons should you review before starting?
The statement does not say which actions it asks for, and this list does not try to point them out either. It gathers, in the order of the course, the lessons that teach an action useful here. Start by rereading those where your last labs were difficult.
- Organize the networks of a stack
- Persist the data of a recreated stack
- Read logs and attribute saturation
- Back up and restore a Compose application
- Update and roll back without losing data
Take the exam
The lab prepares the machines, gives you the statement, then grades the state in which you leave them. Start it when you have about 60 minutes ahead of you, so that you can work in one go.
After the exam
If you pass the threshold without losing the witness record, you can restore a Compose application and its data on another machine on your own, on the points measured. You can move on to the next module. A result under the threshold does not mean that you failed to learn. It shows where the gap is.
The messages of the checks describe the symptom observed, not the action to take. It is up to you to link each failed check to a lesson in the list above, to reread it, then to redo the action yourself. Do not try to memorize an answer.
Key points
- The exam is a measurement. Nothing is explained again, hints cost points and the grade covers the final state of the system.
- The grading ignores the commands you typed. It looks at what is running, what responds, what is served and what the engine has put in place.
- You need 75 points to pass, that is three checks out of four with no hint. A witness record not served by the restored stack fails the exam whatever the total.
- Measuring the real state before rebuilding is the first action of a restoration.
- To close a gap, reread the matching lesson, then redo the action.