style95 commented on a change in pull request #4910:
URL: https://github.com/apache/openwhisk/pull/4910#discussion_r627988832
##########
File path: docs/actions.md
##########
@@ -82,6 +82,84 @@ You can create a new runtime in two ways:
Follow the instructions in [Updating Action Language
Runtimes](actions-update.md) for updating, removing or renaming
runtime kinds or language families.
+### How prewarm containers are provisioned without a reactive configuration
+
+Prewarmed containers are created when invoker starts, they are created
according to runtimes.json's stemCells, e.g.
Review comment:
```suggestion
Prewarmed containers are created when an invoker starts, they are created
according to runtimes.json's stemCells, e.g.
```
##########
File path: docs/actions.md
##########
@@ -82,6 +82,84 @@ You can create a new runtime in two ways:
Follow the instructions in [Updating Action Language
Runtimes](actions-update.md) for updating, removing or renaming
runtime kinds or language families.
+### How prewarm containers are provisioned without a reactive configuration
+
+Prewarmed containers are created when invoker starts, they are created
according to runtimes.json's stemCells, e.g.
+```
+{
+ "kind": "nodejs:14",
+ "default": true,
+ "image": {
+ "prefix": "openwhisk",
+ "name": "action-nodejs-v14",
+ "tag": "nightly"
+ },
+ "deprecated": false,
+ "attached": {
+ "attachmentName": "codefile",
+ "attachmentType": "text/plain"
+ },
+ "stemCells": [
+ {
+ "initialCount": 2,
+ "memory": "256 MB"
+ }
+ ]
+}
+```
+In the above example, there is only one runtime configuration, which is
`nodejs:14`.
+It has a stem cell configuration and 2 containers with 256MB memory for
`nodejs:14` will be provisioned when an invoker starts.
+When an activation with the `nodejs:14` kind arrives, one of the prewarm
containers can be used to alleviate a cold start.
+A prewarm container that is assigned to an action is moved to the busy pool
and the invoker creates one more prewarm container to replenish the prewarm
pool.
+In this way, when no reactive configuration is configured, an invoker always
maintains the same number of prewarm containers.
+
+### How prewarmed containers are provisioned with a reactive configuration
+
+With a reactive configuration, the number of prewarm containers is dynamically
controlled, e.g.
+```
+{
+ "kind": "nodejs:14",
+ "default": true,
+ "image": {
+ "prefix": "openwhisk",
+ "name": "action-nodejs-v14",
+ "tag": "nightly"
+ },
+ "deprecated": false,
+ "attached": {
+ "attachmentName": "codefile",
+ "attachmentType": "text/plain"
+ },
+ "stemCells": [
+ {
+ "initialCount": 2,
+ "memory": "256 MB",
+ "reactive": {
+ "minCount": 1,
+ "maxCount": 4,
+ "ttl": "2 minutes",
+ "threshold": 2,
+ "increment": 1
+ }
+ ]
+}
+```
+In the above example, there is a reactive configuration for `nodejs:14` and
there are 4 underlying configurations.
+* `minCount`: the minimum number of prewarm containers. The number of prewarm
containers can't be fewer than this value
+* `maxCount`: the maximum number of prewarm containers. The number of prewarm
containers cannot exceed this value
+* `ttl`: the amount of time that prewarm containers can exist without any
activation. If no activation for the prewarm container arrives in the given
time, the prewarm container will be removed
+* `threshold` and `increment`: these two configurations control the number of
new prewarm containers to be created.
+
+The number of prewarmed containers is dynamically controlled when:
+* they are expired due to a TTL, some prewarmed containers are removed to save
resources.
+* cold starts happen, some prewarm containers are created according to the
following calculus
Review comment:
```suggestion
* cold starts happen, some prewarm containers are created according to the
following calculus.
```
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