cgroups: Add FallbackToOldVersion to support old cgroups config

Once the new configuration rolls out, we need to support old
configurations for the time being until 16.0 when we can deprecate the
old cgroups config. Until then, allow for a translation layer that
translates the old version to the new version.

4 files changed, 168 insertions, 27 deletions

diff --git a/internal/gitaly/config/cgroups/cgroups.go b/internal/gitaly/config/cgroups/cgroups.go
index 00fb9f45e..935a1a565 100644
--- a/internal/gitaly/config/cgroups/cgroups.go
+++ b/internal/gitaly/config/cgroups/cgroups.go
@@ -22,6 +22,22 @@ type Config struct {
 	Memory Memory `toml:"memory"`
 }
 
+// FallbackToOldVersion translates the old format of cgroups into the new
+// format.
+func (c *Config) FallbackToOldVersion() {
+	if c.Repositories.Count == 0 {
+		c.Repositories.Count = c.Count
+
+		if c.Repositories.MemoryBytes == 0 && c.Memory.Enabled {
+			c.Repositories.MemoryBytes = c.Memory.Limit
+		}
+
+		if c.Repositories.CPUShares == 0 && c.CPU.Enabled {
+			c.Repositories.CPUShares = c.CPU.Shares
+		}
+	}
+}
+
 // Repositories configures cgroups to be created that are isolated by repository.
 type Repositories struct {
 	// Count is the number of cgroups that will be created for repository-level isolation
diff --git a/internal/gitaly/config/cgroups/cgroups_test.go b/internal/gitaly/config/cgroups/cgroups_test.go
new file mode 100644
index 000000000..8b8bdf8cb
--- /dev/null
+++ b/internal/gitaly/config/cgroups/cgroups_test.go
@@ -0,0 +1,150 @@
+package cgroups
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFallbackToOldVersion(t *testing.T) {
+	testCases := []struct {
+		desc         string
+		configBefore Config
+		configAfter  Config
+	}{
+		{
+			desc:         "empty config",
+			configBefore: Config{},
+			configAfter:  Config{},
+		},
+		{
+			desc: "new format",
+			configBefore: Config{
+				Mountpoint:    "some/mountpoint",
+				HierarchyRoot: "gitaly",
+				Repositories: Repositories{
+					Count:       100,
+					MemoryBytes: 1024,
+					CPUShares:   16,
+				},
+			},
+			configAfter: Config{
+				Mountpoint:    "some/mountpoint",
+				HierarchyRoot: "gitaly",
+				Repositories: Repositories{
+					Count:       100,
+					MemoryBytes: 1024,
+					CPUShares:   16,
+				},
+			},
+		},
+		{
+			desc: "old format",
+			configBefore: Config{
+				Mountpoint:    "some/mountpoint",
+				HierarchyRoot: "gitaly",
+				Count:         100,
+				Memory: Memory{
+					Enabled: true,
+					Limit:   1024,
+				},
+				CPU: CPU{
+					Enabled: true,
+					Shares:  16,
+				},
+			},
+			configAfter: Config{
+				Mountpoint:    "some/mountpoint",
+				HierarchyRoot: "gitaly",
+				Count:         100,
+				Memory: Memory{
+					Enabled: true,
+					Limit:   1024,
+				},
+				CPU: CPU{
+					Enabled: true,
+					Shares:  16,
+				},
+				Repositories: Repositories{
+					Count:       100,
+					MemoryBytes: 1024,
+					CPUShares:   16,
+				},
+			},
+		},
+		{
+			desc: "old format, memory only",
+			configBefore: Config{
+				Mountpoint:    "some/mountpoint",
+				HierarchyRoot: "gitaly",
+				Count:         100,
+				Memory: Memory{
+					Enabled: true,
+					Limit:   1024,
+				},
+				CPU: CPU{
+					Enabled: false,
+					Shares:  16,
+				},
+			},
+			configAfter: Config{
+				Mountpoint:    "some/mountpoint",
+				HierarchyRoot: "gitaly",
+				Count:         100,
+				Memory: Memory{
+					Enabled: true,
+					Limit:   1024,
+				},
+				CPU: CPU{
+					Enabled: false,
+					Shares:  16,
+				},
+
+				Repositories: Repositories{
+					Count:       100,
+					MemoryBytes: 1024,
+				},
+			},
+		},
+		{
+			desc: "old format, cpu only",
+			configBefore: Config{
+				Mountpoint:    "some/mountpoint",
+				HierarchyRoot: "gitaly",
+				Count:         100,
+				Memory: Memory{
+					Enabled: false,
+					Limit:   1024,
+				},
+				CPU: CPU{
+					Enabled: true,
+					Shares:  16,
+				},
+			},
+			configAfter: Config{
+				Mountpoint:    "some/mountpoint",
+				HierarchyRoot: "gitaly",
+				Count:         100,
+				Memory: Memory{
+					Enabled: false,
+					Limit:   1024,
+				},
+				CPU: CPU{
+					Enabled: true,
+					Shares:  16,
+				},
+				Repositories: Repositories{
+					Count:     100,
+					CPUShares: 16,
+				},
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *testing.T) {
+			tc.configBefore.FallbackToOldVersion()
+			assert.Equal(t, tc.configAfter, tc.configBefore)
+		})
+	}
+}
diff --git a/internal/gitaly/config/config.go b/internal/gitaly/config/config.go
index 505a0fb9d..bad2091fc 100644
--- a/internal/gitaly/config/config.go
+++ b/internal/gitaly/config/config.go
@@ -291,6 +291,8 @@ func (cfg *Cfg) setDefaults() error {
 		cfg.Cgroups.HierarchyRoot = "gitaly"
 	}
 
+	cfg.Cgroups.FallbackToOldVersion()
+
 	return nil
 }
 
diff --git a/internal/gitaly/config/config_test.go b/internal/gitaly/config/config_test.go
index bbb348e60..a5d15003e 100644
--- a/internal/gitaly/config/config_test.go
+++ b/internal/gitaly/config/config_test.go
@@ -932,33 +932,6 @@ func TestValidateCgroups(t *testing.T) {
 				},
 			},
 			{
-				name: "memory limit - negative",
-				rawCfg: `[cgroups]
-				count = 10
-				mountpoint = "/sys/fs/cgroup"
-				hierarchy_root = "gitaly"
-				[cgroups.memory]
-				enabled = true
-				limit = -5
-				[cgroups.cpu]
-				enabled = true
-				shares = 512
-				`,
-				expect: cgroups.Config{
-					Count:         10,
-					Mountpoint:    "/sys/fs/cgroup",
-					HierarchyRoot: "gitaly",
-					Memory: cgroups.Memory{
-						Enabled: true,
-						Limit:   -5,
-					},
-					CPU: cgroups.CPU{
-						Enabled: true,
-						Shares:  512,
-					},
-				},
-			},
-			{
 				name: "repositories - zero count",
 				rawCfg: `[cgroups]
 				mountpoint = "/sys/fs/cgroup"