{tv 2 => krebs 3} backup

1 files changed, 286 insertions, 0 deletions

diff --git a/krebs/3modules/backup.nix b/krebs/3modules/backup.nix
new file mode 100644
index 00000000..01bb16a2
--- /dev/null
+++ b/krebs/3modules/backup.nix
@@ -0,0 +1,286 @@
+{ config, lib, pkgs, ... }:
+with lib;
+let
+  out = {
+    options.krebs.backup = api;
+    config = mkIf cfg.enable imp;
+  };
+
+  cfg = config.krebs.backup;
+
+  api = {
+    enable = mkEnableOption "krebs.backup" // { default = true; };
+    plans = mkOption {
+      default = {};
+      type = types.attrsOf (types.submodule ({
+        # TODO enable = mkEnableOption "TODO" // { default = true; };
+        options = {
+          method = mkOption {
+            type = types.enum ["pull" "push"];
+          };
+          name = mkOption {
+            type = types.str;
+          };
+          src = mkOption {
+            type = types.krebs.file-location;
+          };
+          dst = mkOption {
+            type = types.krebs.file-location;
+          };
+          startAt = mkOption {
+            type = types.str;
+          };
+          snapshots = mkOption {
+            type = types.attrsOf (types.submodule {
+              options = {
+                format = mkOption {
+                  type = types.str; # TODO date's +FORMAT
+                };
+                retain = mkOption {
+                  type = types.nullOr types.int;
+                  default = null; # null = retain all snapshots
+                };
+              };
+            });
+          };
+        };
+      }));
+    };
+  };
+
+  imp = {
+    users.groups.backup.gid = genid "backup";
+    users.users = {}
+      // {
+        root.openssh.authorizedKeys.keys =
+          map (plan: plan.dst.host.ssh.pubkey)
+              (filter isPullSrc (attrValues cfg.plans))
+          ++
+          map (plan: plan.src.host.ssh.pubkey)
+              (filter isPushDst (attrValues cfg.plans))
+          ;
+      }
+      ;
+    systemd.services =
+      flip mapAttrs' (filterAttrs (_:isPullDst) cfg.plans) (name: plan: {
+        name = "backup.${name}.pull";
+        value = makePullService plan;
+      })
+      //
+      flip mapAttrs' (filterAttrs (_:isPushSrc) cfg.plans) (name: plan: {
+        name = "backup.${name}.push";
+        value = makePushService plan;
+      })
+      ;
+  };
+
+  isPushSrc = plan:
+    plan.method == "push" &&
+    plan.src.host.name == config.krebs.build.host.name;
+
+  isPullSrc = plan:
+    plan.method == "pull" &&
+    plan.src.host.name == config.krebs.build.host.name;
+
+  isPushDst = plan:
+    plan.method == "push" &&
+    plan.dst.host.name == config.krebs.build.host.name;
+
+  isPullDst = plan:
+    plan.method == "pull" &&
+    plan.dst.host.name == config.krebs.build.host.name;
+
+  # TODO push destination needs this in the dst.user's PATH
+  service-path = [
+    pkgs.coreutils
+    pkgs.gnused
+    pkgs.openssh
+    pkgs.rsync
+    pkgs.utillinux
+  ];
+
+  # TODO if there is plan.user, then use its privkey
+  makePushService = plan: assert isPushSrc plan; {
+    path = service-path;
+    serviceConfig = {
+      ExecStart = push plan;
+      Type = "oneshot";
+    };
+    startAt = plan.startAt;
+  };
+
+  makePullService = plan: assert isPullDst plan; {
+    path = service-path;
+    serviceConfig = {
+      ExecStart = pull plan;
+      Type = "oneshot";
+    };
+    startAt = plan.startAt;
+  };
+
+  push = plan: let
+    # We use writeDashBin and return the absolute path so systemd will produce
+    # nice names in the log, i.e. without the Nix store hash.
+    out = "${main}/bin/${main.name}";
+
+    main = writeDashBin "backup.${plan.name}.push" ''
+      set -efu
+      dst=${shell.escape plan.dst.path}
+
+      mkdir -m 0700 -p "$dst"
+      exec flock -n "$dst" ${critical-section}
+    '';
+
+    critical-section = writeDash "backup.${plan.name}.push.critical-section" ''
+      # TODO check if there is a previous
+      set -efu
+      identity=${shell.escape plan.src.host.ssh.privkey.path}
+      src=${shell.escape plan.src.path}
+      dst_target=${shell.escape "root@${getFQDN plan.dst.host}"}
+      dst_path=${shell.escape plan.dst.path}
+      dst=$dst_target:$dst_path
+
+      # Export NOW so runtime of rsync doesn't influence snapshot naming.
+      export NOW
+      NOW=$(date +%s)
+
+      echo >&2 "update snapshot: current; $src -> $dst"
+      rsync >&2 \
+          -aAXF --delete \
+          -e "ssh -F /dev/null -i $identity" \
+          --rsync-path ${shell.escape
+            "mkdir -m 0700 -p ${shell.escape plan.dst.path} && rsync"} \
+          --link-dest="$dst_path/current" \
+          "$src/" \
+          "$dst/.partial"
+
+      exec ssh -F /dev/null \
+          -i "$identity" \
+          "$dst_target" \
+          -T \
+          env NOW="$NOW" /bin/sh < ${remote-snapshot}
+      EOF
+    '';
+
+    remote-snapshot = writeDash "backup.${plan.name}.push.remote-snapshot" ''
+      set -efu
+      dst=${shell.escape plan.dst.path}
+
+      if test -e "$dst/current"; then
+        mv "$dst/current" "$dst/.previous"
+      fi
+      mv "$dst/.partial" "$dst/current"
+      rm -fR "$dst/.previous"
+      echo >&2
+
+      (${(take-snapshots plan).text})
+    '';
+
+  in out;
+
+  # TODO admit plan.dst.user and its ssh identity
+  pull = plan: let
+    # We use writeDashBin and return the absolute path so systemd will produce
+    # nice names in the log, i.e. without the Nix store hash.
+    out = "${main}/bin/${main.name}";
+
+    main = writeDashBin "backup.${plan.name}.pull" ''
+      set -efu
+      dst=${shell.escape plan.dst.path}
+
+      mkdir -m 0700 -p "$dst"
+      exec flock -n "$dst" ${critical-section}
+    '';
+
+    critical-section = writeDash "backup.${plan.name}.pull.critical-section" ''
+      # TODO check if there is a previous
+      set -efu
+      identity=${shell.escape plan.dst.host.ssh.privkey.path}
+      src=${shell.escape "root@${getFQDN plan.src.host}:${plan.src.path}"}
+      dst=${shell.escape plan.dst.path}
+
+      # Export NOW so runtime of rsync doesn't influence snapshot naming.
+      export NOW
+      NOW=$(date +%s)
+
+      echo >&2 "update snapshot: current; $dst <- $src"
+      mkdir -m 0700 -p ${shell.escape plan.dst.path}
+      rsync >&2 \
+          -aAXF --delete \
+          -e "ssh -F /dev/null -i $identity" \
+          --link-dest="$dst/current" \
+          "$src/" \
+          "$dst/.partial"
+      mv "$dst/current" "$dst/.previous"
+      mv "$dst/.partial" "$dst/current"
+      rm -fR "$dst/.previous"
+      echo >&2
+
+      exec ${take-snapshots plan}
+    '';
+  in out;
+
+  take-snapshots = plan: writeDash "backup.${plan.name}.take-snapshots" ''
+    set -efu
+    NOW=''${NOW-$(date +%s)}
+    dst=${shell.escape plan.dst.path}
+
+    snapshot() {(
+      : $ns $format $retain
+      name=$(date --date="@$NOW" +"$format")
+      if ! test -e "$dst/$ns/$name"; then
+        echo >&2 "create snapshot: $ns/$name"
+        mkdir -m 0700 -p "$dst/$ns"
+        rsync >&2 \
+            -aAXF --delete \
+            --link-dest="$dst/current" \
+            "$dst/current/" \
+            "$dst/$ns/.partial.$name"
+        mv "$dst/$ns/.partial.$name" "$dst/$ns/$name"
+        echo >&2
+      fi
+      case $retain in
+        ([0-9]*)
+          delete_from=$(($retain + 1))
+          ls -r "$dst/$ns" \
+            | sed -n "$delete_from,\$p" \
+            | while read old_name; do
+                echo >&2 "delete snapshot: $ns/$old_name"
+                rm -fR "$dst/$ns/$old_name"
+              done
+          ;;
+        (ALL)
+          :
+          ;;
+      esac
+    )}
+
+    ${concatStringsSep "\n" (mapAttrsToList (ns: { format, retain ? null, ... }:
+      toString (map shell.escape [
+        "ns=${ns}"
+        "format=${format}"
+        "retain=${if retain == null then "ALL" else toString retain}"
+        "snapshot"
+      ]))
+      plan.snapshots)}
+  '';
+
+  # TODO getFQDN: admit hosts in other domains
+  getFQDN = host: "${host.name}.${config.krebs.search-domain}";
+
+  writeDash = name: text: pkgs.writeScript name ''
+    #! ${pkgs.dash}/bin/dash
+    ${text}
+  '';
+
+  writeDashBin = name: text: pkgs.writeTextFile {
+    executable = true;
+    destination = "/bin/${name}";
+    name = name;
+    text = ''
+      #! ${pkgs.dash}/bin/dash
+      ${text}
+    '';
+  };
+
+in out