[hotfix] Improve instructions to update playgrounds.
This closes #5.
diff --git a/README.md b/README.md
index 2beaf5d..9226d5e 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@
Currently, the following playgrounds are available:
-* The **Flink Operations Playground** in the (`operations-playground` folder) let's you explore and play with Flink's features to manage and operate stream processing jobs. You can witness how Flink recovers a job from a failure, upgrade and rescale a job, and query job metrics. The playground consists of a Flink cluster, a Kafka cluster and an example
+* The **Flink Operations Playground** in the (`operations-playground` folder) lets you explore and play with Flink's features to manage and operate stream processing jobs. You can witness how Flink recovers a job from a failure, upgrade and rescale a job, and query job metrics. The playground consists of a Flink cluster, a Kafka cluster and an example
Flink job. The playground is presented in detail in the
["Getting Started" guide](https://ci.apache.org/projects/flink/flink-docs-release-1.9/getting-started/docker-playgrounds/flink-operations-playground.html) of Flink's documentation.
diff --git a/howto-update-playgrounds.md b/howto-update-playgrounds.md
index 2885b62..f7d4d2c 100644
--- a/howto-update-playgrounds.md
+++ b/howto-update-playgrounds.md
@@ -1,7 +1,7 @@
# Versioning
-When updating the playgrounds we have to deal with three versions that need to be adjusted.
+When updating the playgrounds we have to deal with three versions that might need to be adjusted.
Externally defined versions:
@@ -14,29 +14,57 @@
# Updating the playgrounds
-## Update playgrounds due to a new minor (or major) Flink release
+## Update playgrounds due to a new bugfix Flink release
-First of all, check that a Flink Docker image was published on [Docker Hub](https://hub.docker.com/_/flink) for the new Flink version.
+Apache Flink bugfix releases are frequently published. For example, Flink 1.8.2 is the second bugfix release in the Flink 1.8 release line. Bugfix releases are binary compatible with previous releases on the same minor release line.
-Update all playgrounds as follows:
+When a new bugfix release is published, we have to wait until the corresponding Flink Docker image is published on [Docker Hub](https://hub.docker.com/_/flink). Once the Flink Docker image is available, update all playgrounds as follows:
1. All `pom.xml`:
* Update the versions of all Flink dependencies
- * Update the Maven artifact version to the new playground version (`1-Flink-1.9` if 1.9.0 is the new Flink release).
- * Check that all Maven projects build.
+ * Update the Maven artifact version to the new playground version (`4-Flink-1.9` is the fourth update of the playground for the Flink 1.9 line).
+ * All Maven projects should still build as bugfix releases should be compatible with previous versions.
2. All `Dockerfile`:
- * Update version of the base image to the new Flink Docker image version.
+ * Update the version of the base image to the new Flink Docker image version.
3. `docker-compose.yaml`:
- * Update the version of the Flink containers to the new Flink docker image version.
* Update the version of the custom Docker images to the new playground version.
+ * Update the version of the Flink containers to the new Flink docker image version if necessary.
-## Update a playground due to bug in a custom Docker image
+The `flink-playgrounds` repository has a branch for every minor Flink release (for example `release-1.9` for all releases of the Flink 1.9 line). Updates for a bugfix release should be pushed to the existing branch of the updated release line.
-Whenever, you need to update a Docker image, please increment the playground version in the following places.
+## Update playgrounds due to a new minor (or major) Flink release
-* the artifact version of all Maven projects in all `pom.xml` files.
-* the tag (name and version) of all custom images in all `docker-compose.yaml` files.
+A major release marks a significant new version of Flink that probably breaks a lot of existing code. For example Flink 2.0.0 would be a major release that starts the Flink 2.x line. A minor release marks a new version of Apache Flink with significant improvements and changes. For example, Flink 1.9.0 is the minor release which starts the Flink 1.9 release line. New minor releases aim to be compatible but might deprecate, evolve, or remove code of previous releases. For updates due to minor and major Flink versions, the same update rules apply.
+
+When a new minor or major release is published, we have to wait until the corresponding Flink Docker image is published on [Docker Hub](https://hub.docker.com/_/flink). Once the Flink Docker image is available, update all playgrounds as follows:
+
+1. All `pom.xml`:
+ * Update the versions of all Flink dependencies
+ * Update the Maven artifact version to the new playground version (`1-Flink-1.9` is the first version of the playground for the Flink 1.9 line).
+ * Check that all Maven projects still build and fix all issues related to the Flink version update.
+2. All `Dockerfile`:
+ * Update the version of the base image to the new Flink Docker image version.
+3. `docker-compose.yaml`:
+ * Update the version of the custom Docker images to the new playground version.
+ * Update the version of the Flink containers to the new Flink docker image version.
+
+The `flink-playgrounds` repository has a branch for every minor Flink release (for example `release-1.9` for all releases of the Flink 1.9 line). A playground update due to a new minor or major Flink release starts a new branch. Moreover, the new version should also be pushed to the `master` branch.
+
+## Update a playground to improve a custom Docker image
+
+You might want to update the software in a Docker image to add a new feature or fix a bug.
+Whenever you update an image you have to increment the playground version in the following places.
+
+* the artifact version of all Maven projects that are modified.
+* the tag (name and version) of all affected custom images the `docker-compose.yaml` files.
+
+The update of the `docker-compose.yaml` file is important to ensure that the updated Docker image gets a new version.
+Otherwise the new image might not be built if a user had run the playground before with an earlier image.
+
+Changes to the playgrounds should be pushed to all affected branches (`release-x.z`, `master`) of the `flink-playgrounds` repository.
## Update a playground without updating a custom Docker image
-Just update the `docker-compose.yaml` file.
+If you want to use a different public (not custom) Docker image, you can just update the `docker-compose.yaml` file.
+
+Changes to the playgrounds should be pushed to all affected branches (`release-x.z`, `master`) of the `flink-playgrounds` repository.
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