epel: allow epel-release to not be installed at all

When DIB_EPEL_DISABLED=2 then the epel element will have no effect at
all, including not installing yum-utils or epel-release packages.

wget is not actually used by the epel element so it has been removed as
a package dependency.

This is to handle scenarios when EPEL is strictly disallowed, so package
install failures are preferred.

Change-Id: Ic6f6c92b28b80c4f0b93e4663129e73134f5b447
Signed-off-by: Steve Baker <sbaker@redhat.com>

diskimage_builder/elements/epel/README.rst

@@ -20,4 +20,5 @@ DIB_EPEL_DISABLED:
    :Required: No
    :Default: 0
    :Description: To disable the EPEL repo (but leave it available if
-                 used with an explicit ``--enablerepo``) set this to 1
+                 used with an explicit ``--enablerepo``) set this to 1.
+                 To avoid installing the epel-release entirely, set this to 2.

diskimage_builder/elements/epel/package-installs.yaml

@@ -1,4 +0,0 @@
-wget:
-  phase: pre-install.d
-yum-utils:
-  phase: pre-install.d

diskimage_builder/elements/epel/pkg-map

@@ -1,20 +1,16 @@
 {
  "distro": {
     "almalinux": {
-       "wget": "wget",
        "yum-utils": "yum-utils"
     },
     "centos": {
-       "wget": "wget",
        "yum-utils": "yum-utils"
     },
     "rocky": {
-       "wget": "wget",
        "yum-utils": "yum-utils"
     }
  },
  "default": {
-   "wget": "",
    "yum-utils": ""
  }
 }

diskimage_builder/elements/epel/pre-install.d/05-rpm-epel-release

@@ -6,16 +6,22 @@ fi
 set -eu
 set -o pipefail
 
+if [ ${DIB_EPEL_DISABLED:-0} -gt 1 ]; then
+    exit 0
+fi
+
+install-packages yum-utils
+
 if [[ (${DISTRO_NAME} =~ "almalinux" || ${DISTRO_NAME} =~ "centos" || ${DISTRO_NAME} =~ "rocky") ]]; then
     # Centos has "epel-release" in extras, which is default enabled.
-    ${YUM} install -y epel-release
+    install-packages epel-release
 else
     echo "$DISTRO_NAME is not supported"
     # Not really a failure; we just don't do anything
     exit 0
 fi
 
-if [ ${DIB_EPEL_DISABLED:-0} -ne 0 ]; then
+if [ ${DIB_EPEL_DISABLED:-0} -gt 0 ]; then
     if [[ ${YUM} == "dnf" ]]; then
         rpm  -q dnf-plugins-core || dnf install -y dnf-plugins-core
         dnf config-manager --set-disabled "epel*"

releasenotes/notes/dib_epel_disabled-55caa271f9959b32.yaml

@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    Previously `DIB_EPEL_DISABLED` was documented to install epel-release
+    but disable the repositories when set to `1`. It is now possible to
+    avoid installing the epel-release package entirely by setting
+    `DIB_EPEL_DISABLED` to `2`. This is to accomodate scenarios where
+    using EPEL is strictly forbidden.