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fix: reduce legacy Linux custom data encoding overhead #9880

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18c6ca8
fix: reduce legacy Linux custom data encoding overhead
sinmentis Oct 23, 2026
d4da1bb
refactor: extract cloud-init encoding and test helpers
sinmentis Oct 23, 2026
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3 changes: 2 additions & 1 deletion hotfix/hotfix_generate_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -161,7 +161,8 @@ def test_config_modules_are_independently_hotfixable(self):
self.assertEqual({variable}, blocks[0][0])
self.assertIn(f"- path: {{{{{path_function}}}}}", template)
self.assertIn('permissions: "0744"', template)
self.assertIn("encoding: gzip", template)
self.assertIn("encoding: {{GetCloudInitFileEncoding}}", template)
self.assertIn("| GetCloudInitFileContent}}", template)
self.assertNotIn("{{if", template)

def test_mariner_package_update_is_not_embedded_in_custom_data(self):
Expand Down
16 changes: 8 additions & 8 deletions hotfix/render-nodecustomdata/main_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -18,18 +18,16 @@ func TestRenderSelectedHotfixScripts(t *testing.T) {
const initCloudBlock = `{{if IsAKSCustomCloud}}
- path: {{GetInitAKSCloudFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "initAKSCloud"}}
content: {{GetVariableProperty "cloudInitData" "initAKSCloud" | GetCloudInitFileContent}}
{{end}}
`
const helperBlock = `- path: {{GetCSEHelpersScriptFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionSource"}}
content: {{GetVariableProperty "cloudInitData" "provisionSource" | GetCloudInitFileContent}}
`
for _, distro := range []datamodel.Distro{
datamodel.AKSUbuntuContainerd2204Gen2,
Expand All @@ -47,8 +45,9 @@ func TestRenderSelectedHotfixScripts(t *testing.T) {
require.NoError(t, err)
var payload struct {
WriteFiles []struct {
Path string `yaml:"path"`
Content string `yaml:"content"`
Path string `yaml:"path"`
Encoding string `yaml:"encoding"`
Content string `yaml:"content"`
} `yaml:"write_files"`
}
require.NoError(t, yaml.Unmarshal([]byte(rendered), &payload))
Expand All @@ -62,6 +61,7 @@ func TestRenderSelectedHotfixScripts(t *testing.T) {
require.Len(t, payload.WriteFiles, 1+wantInitCount)
for _, file := range payload.WriteFiles {
require.NotEmpty(t, file.Content)
require.Empty(t, file.Encoding)
}
})
}
Expand Down
135 changes: 54 additions & 81 deletions parts/linux/cloud-init/nodecustomdata.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -28,201 +28,174 @@ write_files:
{{if IsAKSCustomCloud}}
- path: {{GetInitAKSCloudFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "initAKSCloud"}}
content: {{GetVariableProperty "cloudInitData" "initAKSCloud" | GetCloudInitFileContent}}
{{end}}

{{- else }}
- path: {{GetCSEHelpersScriptFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionSource"}}
content: {{GetVariableProperty "cloudInitData" "provisionSource" | GetCloudInitFileContent}}


{{if IsACL }}
- path: {{GetCSEHelpersScriptDistroFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionSourceACL"}}
content: {{GetVariableProperty "cloudInitData" "provisionSourceACL" | GetCloudInitFileContent}}
{{- else if IsAzlOSGuard}}
- path: {{GetCSEHelpersScriptDistroFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionSourceAzlOSGuard"}}
content: {{GetVariableProperty "cloudInitData" "provisionSourceAzlOSGuard" | GetCloudInitFileContent}}
{{- else if IsMariner}}
- path: {{GetCSEHelpersScriptDistroFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionSourceMariner"}}
content: {{GetVariableProperty "cloudInitData" "provisionSourceMariner" | GetCloudInitFileContent}}
{{- else if IsFlatcar }}
- path: {{GetCSEHelpersScriptDistroFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionSourceFlatcar"}}
content: {{GetVariableProperty "cloudInitData" "provisionSourceFlatcar" | GetCloudInitFileContent}}
{{- else }}
- path: {{GetCSEHelpersScriptDistroFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionSourceUbuntu"}}
content: {{GetVariableProperty "cloudInitData" "provisionSourceUbuntu" | GetCloudInitFileContent}}
{{end}}

{{ if not IsCustomImage -}}
- path: /opt/azure/containers/provision_start.sh
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionStartScript"}}
content: {{GetVariableProperty "cloudInitData" "provisionStartScript" | GetCloudInitFileContent}}
{{- end }}

- path: /opt/azure/containers/provision.sh
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionScript"}}
content: {{GetVariableProperty "cloudInitData" "provisionScript" | GetCloudInitFileContent}}

- path: {{GetCSEInstallScriptFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionInstalls"}}
content: {{GetVariableProperty "cloudInitData" "provisionInstalls" | GetCloudInitFileContent}}

{{if IsACL }}
- path: {{GetCSEInstallScriptDistroFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionInstallsACL"}}
content: {{GetVariableProperty "cloudInitData" "provisionInstallsACL" | GetCloudInitFileContent}}
{{- else if IsAzlOSGuard}}
- path: {{GetCSEInstallScriptDistroFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionInstallsAzlOSGuard"}}
content: {{GetVariableProperty "cloudInitData" "provisionInstallsAzlOSGuard" | GetCloudInitFileContent}}
{{- else if IsMariner}}
- path: {{GetCSEInstallScriptDistroFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionInstallsMariner"}}
content: {{GetVariableProperty "cloudInitData" "provisionInstallsMariner" | GetCloudInitFileContent}}
{{- else if IsFlatcar }}
- path: {{GetCSEInstallScriptDistroFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionInstallsFlatcar"}}
content: {{GetVariableProperty "cloudInitData" "provisionInstallsFlatcar" | GetCloudInitFileContent}}
{{- else }}
- path: {{GetCSEInstallScriptDistroFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionInstallsUbuntu"}}
content: {{GetVariableProperty "cloudInitData" "provisionInstallsUbuntu" | GetCloudInitFileContent}}
{{end}}

- path: {{GetCSEConfigScriptFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionConfigs"}}
content: {{GetVariableProperty "cloudInitData" "provisionConfigs" | GetCloudInitFileContent}}

- path: {{GetCSEConfigGPUScriptFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionConfigsGPU"}}
content: {{GetVariableProperty "cloudInitData" "provisionConfigsGPU" | GetCloudInitFileContent}}

- path: {{GetCSEConfigLocalDNSScriptFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionConfigsLocalDNS"}}
content: {{GetVariableProperty "cloudInitData" "provisionConfigsLocalDNS" | GetCloudInitFileContent}}

- path: {{GetCSEConfigKubeletScriptFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionConfigsKubelet"}}
content: {{GetVariableProperty "cloudInitData" "provisionConfigsKubelet" | GetCloudInitFileContent}}

- path: {{GetCSEConfigNetworkScriptFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionConfigsNetwork"}}
content: {{GetVariableProperty "cloudInitData" "provisionConfigsNetwork" | GetCloudInitFileContent}}

- path: {{GetCSEConfigAddonsScriptFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionConfigsAddons"}}
content: {{GetVariableProperty "cloudInitData" "provisionConfigsAddons" | GetCloudInitFileContent}}

- path: {{GetCSEConfigChronyScriptFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "provisionConfigsChrony"}}
content: {{GetVariableProperty "cloudInitData" "provisionConfigsChrony" | GetCloudInitFileContent}}

{{if IsAKSCustomCloud}}
- path: {{GetInitAKSCloudFilepath}}
permissions: "0744"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "initAKSCloud"}}
content: {{GetVariableProperty "cloudInitData" "initAKSCloud" | GetCloudInitFileContent}}
{{end}}

- path: /etc/systemd/system/reconcile-private-hosts.service
permissions: "0644"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "reconcilePrivateHostsService"}}
content: {{GetVariableProperty "cloudInitData" "reconcilePrivateHostsService" | GetCloudInitFileContent}}

- path: /etc/systemd/system/kubelet.service
permissions: "0600"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "kubeletSystemdService"}}
content: {{GetVariableProperty "cloudInitData" "kubeletSystemdService" | GetCloudInitFileContent}}

- path: /opt/azure-network/configure-azure-network.sh
permissions: "0755"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "configureAzureNetworkScript"}}
content: {{GetVariableProperty "cloudInitData" "configureAzureNetworkScript" | GetCloudInitFileContent}}

- path: /etc/udev/rules.d/99-azure-network.rules
permissions: "0644"
encoding: gzip
encoding: {{GetCloudInitFileEncoding}}
owner: root
content: !!binary |
{{GetVariableProperty "cloudInitData" "azureNetworkUdevRule"}}
content: {{GetVariableProperty "cloudInitData" "azureNetworkUdevRule" | GetCloudInitFileContent}}
{{- end }}
50 changes: 41 additions & 9 deletions pkg/agent/baker.go
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Original file line number Diff line number Diff line change
Expand Up @@ -346,17 +346,20 @@ func buildScriptlessCustomData(cloudInitTemplate, fileListTemplate, separator st
// GetLinuxNodeCustomDataJSONObject returns Linux customData JSON object in the form.
// { "customData": "<customData string>" }.
func (t *TemplateGenerator) getLinuxNodeCustomDataJSONObject(config *datamodel.NodeBootstrappingConfiguration) string {
// get parameters
parameters := getParameters(config)
// get variable cloudInit
variables := getCustomDataVariables(config)
str, e := t.getSingleLineForTemplate(kubernetesNodeCustomDataYaml, config.AgentPoolProfile, getBakerFuncMap(config, parameters, variables), true)

if e != nil {
panic(e)
b, err := parts.Templates.ReadFile(kubernetesNodeCustomDataYaml)
if err != nil {
panic(err)
}
str, err := RenderLinuxNodeCustomDataTemplate(b, config)
if err != nil {
panic(err)
}

return fmt.Sprintf("{\"customData\": \"%s\"}", str)
customData, err := json.Marshal(map[string]string{"customData": str})
if err != nil {
panic(err)
}
return string(customData)
}

const (
Expand Down Expand Up @@ -677,6 +680,8 @@ func (t *TemplateGenerator) getSingleLine(textFilename string, profile interface
// same variables and functions used by the production AgentBaker path.
// Callers must supply a complete configuration, as required by the production
// rendering helpers.
// File entries must use GetCloudInitFileEncoding and GetCloudInitFileContent
// to select the encoding for the delivery mode.
func RenderLinuxNodeCustomDataTemplate(templateContent []byte, config *datamodel.NodeBootstrappingConfiguration) (string, error) {
parameters := getParameters(config)
variables := getCustomDataVariables(config)
Expand All @@ -694,10 +699,37 @@ func RenderLinuxNodeCustomDataTemplate(templateContent []byte, config *datamodel
return buffer.String(), nil
}

// Traditional custom data is gzipped as a whole, so its files need no inner encoding.
func usePlainCloudInit(config *datamodel.NodeBootstrappingConfiguration) bool {
return !config.EnableScriptlessCSECmd && !config.IsFlatcar() && !config.IsACL()
}

func getCloudInitFileEncoding(config *datamodel.NodeBootstrappingConfiguration) string {
if usePlainCloudInit(config) {
return `""`
}
return encodingGZIP
}

func getCloudInitFileContent(config *datamodel.NodeBootstrappingConfiguration, content string) (string, error) {
if usePlainCloudInit(config) {
encoded, err := json.Marshal(content)

@awesomenix Nishchay (awesomenix) Oct 24, 2026

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I am worried about this line, marshalling plain text in json, i am worried that some introduction of text might break this in future.

return string(encoded), err
}
return "!!binary |\n " + content, nil
}

// getTemplateFuncMap returns the general purpose template func map from getContainerServiceFuncMap.
func getBakerFuncMap(config *datamodel.NodeBootstrappingConfiguration, params paramsMap, variables paramsMap) template.FuncMap {
funcMap := getContainerServiceFuncMap(config)

funcMap["GetCloudInitFileEncoding"] = func() string {
return getCloudInitFileEncoding(config)
}
funcMap["GetCloudInitFileContent"] = func(content string) (string, error) {
return getCloudInitFileContent(config, content)
}

funcMap["GetParameter"] = func(s string) interface{} {
if v, ok := params[s].(paramsMap); ok && v != nil {
if v["value"] == nil {
Expand Down
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