Resolves #431 - Add support for dynamic runbook steps

docs/runbook-development.md

@@ -4,6 +4,8 @@
 
 This document outlines the syntax and capabilities of runbooks. 
 
+
+
 ## Prerequisites
 
 Users developing runbooks should have familiarity with:
@@ -158,6 +160,72 @@ epcc create customer-address  "Hello World" name "address_0" first_name "John" l
 epcc create customer-address  "Hello World" name "address_1" first_name "John" last_name "Smith" line_1 "1234 Main Street" county "XX" "postcode" "H0H 0H0" country "DE"
 ```
 
+### Dynamic Steps
+
+Templates are only renderable for a particular step, but you can instead of generating a command, actually generate a Yaml array, that will be interpreted as steps.
+This can give you more control over control flow, where-as otherwise you are stuck with all rendered commands being in the same sequence.
+
+```yaml
+name: hello-world
+description:
+  short: "A hello world runbook"
+actions:
+   sequential-sleeps:
+   variables:
+      count:
+         type: INT
+         default: 2
+         description:
+            short: "The number of sleeps"
+   commands:
+      - |2
+        {{- range untilStep 0 .count 1}}
+          - sleep 1
+        {{- end -}}
+   concurrent-sleeps:
+      variables:
+         count:
+            type: INT
+            default: 2
+            description:
+               short: "The number of sleeps"
+      commands:
+         - |
+            {{- range untilStep 0 .count 1}}
+            sleep 1
+            {{- end -}}
+```
+
+It's important for all commands to be indended the same amount, and start with a `-` this will cause the entire string to be valid as a Yaml array.
+
+You can see the results of executing these runbooks below, without the `-` the commands all execute concurrently. With the `-` the execute one after another.
+
+```bash
+$time epcc runbooks run hello-world concurrent-sleeps  --count 4
+INFO[0000] Executing> {{- range untilStep 0 .count 1}}
+sleep 1
+{{- end -}} 
+INFO[0000] Sleeping for 1 seconds                       
+INFO[0000] Sleeping for 1 seconds                       
+INFO[0000] Sleeping for 1 seconds                       
+INFO[0000] Sleeping for 1 seconds                       
+real    0m1.302s
+user    0m0.441s
+sys     0m0.059s
+$time epcc runbooks run hello-world sequential-sleeps --count 4
+INFO[0000] Executing> sleep 1                           
+INFO[0000] Sleeping for 1 seconds                       
+INFO[0001] Executing> sleep 1                           
+INFO[0001] Sleeping for 1 seconds                       
+INFO[0002] Executing> sleep 1                           
+INFO[0002] Sleeping for 1 seconds                       
+INFO[0003] Executing> sleep 1                           
+INFO[0003] Sleeping for 1 seconds                       
+real    0m4.289s
+user    0m0.405s
+sys     0m0.050s
+```
+
 ### Error Handling
 
 By default, an error in a command will stop execution, when operating concurrently all commands will finish in that block, and then abort. In some cases, it may be the case that errors are unavoidable, in which case the **ignore_errors** block can be used. In the future more granular error handling could be implemented based on need.