Drone uses the `matrix` section of the `.drone.yml` to define the build matrix. Drone executes a build for each permutation in the matrix, allowing you to build and test a single commit against many configurations.
Below is an example `.drone.yml` that tests a single commit against multiple versions of Go and Redis, resulting in a total of 6 different build permutations:
```yaml
build:
image: golang:$$GO_VERSION
commands:
- go get
- go build
- go test
compose:
redis:
image: redis:$$REDIS_VERSION
matrix:
GO_VERSION:
- 1.4
- 1.3
REDIS_VERSION:
- 2.6
- 2.8
- 3.0
```
## Matrix Variables
Matrix variables are injected into the `.drone.yml` file using the `$$` syntax, performing a simple find / replace. Matrix variables are also injected into your build container as environment variables.
This is an example `.drone.yml` file before injecting the matrix parameters:
```yaml
build:
image: golang:$$GO_VERSION
commands:
- go get
- go build
- go test
compose:
redis:
image: redis:$$REDIS_VERSION
matrix:
GO_VERSION:
- 1.4
REDIS_VERSION:
- 3.0
```
And this is the `.drone.yml` file after injecting the matrix parameters:
```yaml
build:
image: golang:1.4
environment:
- GO_VERSION=1.4
- REDIS_VERSION=3.0
commands:
- go get
- go build
- go test
compose:
redis:
image: redis:3.0
```
## Matrix Deployments
Matrix builds execute the same `.drone.yml` multiple times, but with different parameters. This means that publish and deployment steps are executed multiple times as well, which is typically undesired. To restrict a publish or deployment step to a single permutation you can add the following condition:
