Docker Compose Flashcards
1
Q
Docker Compose Basics
A
- Markdown tool to specify Docker configurations as code
- Procedural
- Declarative
2
Q
Production System Considerations
A
- Multiple Systems
- Microservices
- Third-party dependencies
3
Q
Procedural
A
- Series of ordered steps
- Based on assumptions about the previous step
- Easy to introduce errors
4
Q
Declarative
A
- Specify end results
- System will determine which steps to execute
- Produces the same result each time
5
Q
Main Benefits of Docker Compose
A
- Version control
- Self-documenting
- Easy management
6
Q
Designed For
A
- Local development
- Staging server
- Continuous integration testing environment
7
Q
Not Designed For
A
- Distributed systems
- Complex production environments
- No autoscaling
- Use orchestration tools like Docker Swarm or Kubernetes in production
8
Q
Docker Compose Configuration
A
- Create a file “docker-compose.yaml”
- Version: specifies which version of Docker Compose to use
- Services: specifies which containers are required (specify a path to the corresponding Docker build file or image)
9
Q
Start all services defined in the Docker Compose file
A
- “docker-compose up”
- Pass in a service name to any command to only apply it to that service
10
Q
Stop all containers
A
- “docker-compose down”
- Deletes all containers and images and removes all artifacts
11
Q
Save battery or free memory
A
- “docker-compose stop”
12
Q
Stop and restart all containers
A
- “docker-compose restart”
13
Q
Environment Variables
A
- Accessible inside a running Docker container
- Specify runtime environment
- Use env files if necessary (pass in env file path)
- Including an env variable name without a value will pass in the value from the host server
14
Q
Build Arguments
A
- Accessible only at build times
- Build tool versions
- Cloud platform configuration
15
Q
Target Volume
A
- File directory path inside a container where the volume data lives
16
Q
Source Volume
A
- File directory path on the host machine outside a container where the volume data lives
17
Q
Volume Access Modes
A
- rw: read-write by default
- ro: read-only
18
Q
Mounting Volume Syntax
A
- <source></source>:<TARGET>:<MODE></MODE></TARGET>
19
Q
Named Volumes
A
- Running “docker-compose up” or “docker-compose restart” will automatically copy old volume data to the new container
- Running “docker-compose down –volumes” will automatically delete named volumes
- Without named volumes you can run out of memory
20
Q
Exposing Ports
A
- Map the ports for all containers in the Docker Compose file
21
Q
Enforcing Container Start-Up Order
A
- Add a “depends_on” object under a service definition in the Docker Compose file
- Only guarantees that dependent containers have been started, not that they are healthy and running
22
Q
Advantages of a Single Compose File
A
- Shared containers
- Easier integration testing
- Conceptually one system
23
Q
Named Subsets of Services
A
- List one or more profile names under the profile keyword for a service
- A container with no profiles specified is included by default
- Docker Compose commands will only apply to a service if its profile is explicitly enabled
- Add “–profile <NAME>" to enable a non-default profile</NAME>
24
Q
Multiple Compose Files
A
- Distinct desired behaviors that do not coincide
- Different environments
- By default, Docker Compose will read docker-compose.yaml and docker-compose.override.yaml
- Docker Compose will merge the two files
25
Merge Rules for Compose Files
- Array fields: original + override
- Single-value fields: preference to override
- Override can be a partial or incomplete configuration
26
Run Docker Compose Override
- "docker-compose -f -f "
27
Example Environment Variables
- Image tags
- Software versions
- Ports
28
Accessing Environment Variables
- Use the syntax "${NAME}"
29
Environment Variable Defaults
- Empty string (automatic)
- Inline in docker-compose configuration
- In .env file
- Throw error if missing (no default)
- The host env variable in the shell will always supersede the default
30
Pass in a .env file
- "--env-file "
