Tagging images during build in Docker - Step-by-Step Execution

Process Flow - Tagging images during build

Write Dockerfile

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Run docker build

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Docker reads Dockerfile

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Build image layers

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Assign tag(s) to image

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Image stored locally with tag

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Use tagged image for run/push

This flow shows how Docker reads a Dockerfile, builds the image, and assigns tags during the build command.

Execution Sample

Docker

docker build -t myapp:1.0 -t myapp:latest .

Builds a Docker image from the current directory and tags it as 'myapp:1.0' and 'myapp:latest'.

Process Table

Step	Command Part	Action	Result
1	docker build	Start building image	Docker reads Dockerfile from current directory
2	-t myapp:1.0	Assign first tag	Image will be tagged as 'myapp:1.0'
3	-t myapp:latest	Assign second tag	Image will also be tagged as 'myapp:latest'
4	.	Context path	Docker uses current directory as build context
5	Build process	Execute Dockerfile instructions	Image layers created
6	Tagging	Apply tags to final image	Image stored locally with both tags
7	Finish	Build completes	Image ready to use with tags 'myapp:1.0' and 'myapp:latest'

💡 Build completes successfully with specified tags applied to the image.

Status Tracker

Variable	Start	After Step 2	After Step 3	Final
Image Tags	None	myapp:1.0	myapp:1.0, myapp:latest	myapp:1.0, myapp:latest

Key Moments - 3 Insights

Why do we use multiple -t options in the docker build command?

Each -t option adds a tag to the same image. This lets you refer to the image by different names or versions, as shown in steps 2 and 3 of the execution table.

What does the '.' mean at the end of the docker build command?

The '.' tells Docker to use the current directory as the build context, meaning it looks here for the Dockerfile and any files needed during build (step 4).

When are the tags actually applied to the image?

Tags are applied after the image layers are built, right before storing the image locally (step 6). Before that, the image is being constructed without tags.

Visual Quiz - 3 Questions

Look at the execution table, what tags does the image have after step 3?

A Only myapp:latest

B Only myapp:1.0

C myapp:1.0 and myapp:latest

D No tags yet

💡 Hint

Check the 'Action' and 'Result' columns for step 3 in the execution table.

At which step does Docker start reading the Dockerfile?

A Step 4

B Step 1

C Step 5

D Step 2

💡 Hint

Look at the 'Command Part' and 'Action' columns in the execution table for when the build starts.

If you omit the -t options, what happens to the image tags?

A Image has no tag and is unnamed

B Build fails immediately

C Image gets default 'latest' tag

D Image is tagged with directory name

💡 Hint

Think about Docker's default behavior when no tag is specified during build.

Concept Snapshot

docker build -t name:tag .
Use multiple -t to add several tags.
Tags label the image for easy reference.
The '.' sets the build context directory.
Tags apply after image layers build.
Tagged images can be run or pushed.

Full Transcript

This visual execution shows how Docker builds an image and tags it during the build command. First, Docker reads the Dockerfile from the current directory. Then, each -t option adds a tag to the image. The build context is set by the '.' meaning current folder. Docker executes the Dockerfile instructions to create image layers. After building, Docker applies the tags to the image and stores it locally. The image can then be used by referring to any of its tags. This process helps organize images by version or purpose.