- Layer is basically a change on an image, or an intermediate image.
- Every instructions you specify (FROM, RUN, COPY, etc.) in your Dockerfile causes the previous image to change, thus creating a new layer.
- That image layer then becomes the parent for the layer created by the next instruction.
- Final image and/or image that we use consists of a series of layers which are stacked, one on top of the another.
- You can think of it as staging changes when you're using git. You add a file's change, then another one, then another one.
- When you build your image before, you also created lots of images.
docker build . -t docker-kubernetes:dockerfile-basics
+---------------------------------+
+------------> | 6e384ad670e7 |
| | CMD ["java", "-jar", "app.jar"] |
| +---------------------------------+
+------------> | adfedcd08e78 |
| |COPY ["target/*.jar", "./app.jar"|
| +---------------------------------+
+------------> | aae885b8525e |
Layer Id+----+ | RUN apk add --no-cache curl |
| +---------------------------------+
+------------> | 14446213dae8 |
| | EXPOSE 8080 |
| +---------------------------------+
+------------> | a40643187675 |
| | WORKDIR /myApp |
| +---------------------------------+
+------------> | 1b46cc2ba839 |
| FROM openjdk:8-jre-alpine |
+---------------------------------+