feat: support parallel with execution order groups (#2403)

runatlantis.io/docs/repo-level-atlantis-yaml.md

@@ -214,6 +214,8 @@ projects:
 ```
 With this config above, Atlantis runs planning/applying for project2 first, then for project1.
 Several projects can have same `execution_order_group`. Any order in one group isn't guaranteed.
+`parallel_plan` and `parallel_apply` respect these order groups, so parallel planning/applying works 
+in each group one by one.
 
 ### Custom Backend Config
 See [Custom Workflow Use Cases: Custom Backend Config](custom-workflows.html#custom-backend-config)

server/events/apply_command_runner.go

@@ -144,7 +144,7 @@ func (a *ApplyCommandRunner) Run(ctx *command.Context, cmd *CommentCommand) {
 	var result command.Result
 	if a.isParallelEnabled(projectCmds) {
 		ctx.Log.Info("Running applies in parallel")
-		result = runProjectCmdsParallel(projectCmds, a.prjCmdRunner.Apply, a.parallelPoolSize)
+		result = runProjectCmdsParallelGroups(projectCmds, a.prjCmdRunner.Apply, a.parallelPoolSize)
 	} else {
 		result = runProjectCmds(projectCmds, a.prjCmdRunner.Apply)
 	}

server/events/plan_command_runner.go

@@ -110,7 +110,7 @@ func (p *PlanCommandRunner) runAutoplan(ctx *command.Context) {
 	var result command.Result
 	if p.isParallelEnabled(projectCmds) {
 		ctx.Log.Info("Running plans in parallel")
-		result = runProjectCmdsParallel(projectCmds, p.prjCmdRunner.Plan, p.parallelPoolSize)
+		result = runProjectCmdsParallelGroups(projectCmds, p.prjCmdRunner.Plan, p.parallelPoolSize)
 	} else {
 		result = runProjectCmds(projectCmds, p.prjCmdRunner.Plan)
 	}
@@ -184,7 +184,7 @@ func (p *PlanCommandRunner) run(ctx *command.Context, cmd *CommentCommand) {
 	var result command.Result
 	if p.isParallelEnabled(projectCmds) {
 		ctx.Log.Info("Running applies in parallel")
-		result = runProjectCmdsParallel(projectCmds, p.prjCmdRunner.Plan, p.parallelPoolSize)
+		result = runProjectCmdsParallelGroups(projectCmds, p.prjCmdRunner.Plan, p.parallelPoolSize)
 	} else {
 		result = runProjectCmds(projectCmds, p.prjCmdRunner.Plan)
 	}

server/events/project_command_pool_executor.go

@@ -1,6 +1,7 @@
 package events
 
 import (
+	"sort"
 	"sync"
 
 	"github.com/remeh/sizedwaitgroup"
@@ -50,3 +51,37 @@ func runProjectCmds(
 	}
 	return command.Result{ProjectResults: results}
 }
+
+func splitByExecutionOrderGroup(cmds []command.ProjectContext) [][]command.ProjectContext {
+	groups := make(map[int][]command.ProjectContext)
+	for _, cmd := range cmds {
+		groups[cmd.ExecutionOrderGroup] = append(groups[cmd.ExecutionOrderGroup], cmd)
+	}
+
+	var groupKeys []int
+	for k := range groups {
+		groupKeys = append(groupKeys, k)
+	}
+	sort.Ints(groupKeys)
+
+	var res [][]command.ProjectContext
+	for _, group := range groupKeys {
+		res = append(res, groups[group])
+	}
+	return res
+}
+
+func runProjectCmdsParallelGroups(
+	cmds []command.ProjectContext,
+	runnerFunc prjCmdRunnerFunc,
+	poolSize int,
+) command.Result {
+	var results []command.ProjectResult
+	groups := splitByExecutionOrderGroup(cmds)
+	for _, group := range groups {
+		res := runProjectCmdsParallel(group, runnerFunc, poolSize)
+		results = append(results, res.ProjectResults...)
+	}
+
+	return command.Result{ProjectResults: results}
+}