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Put a file in a Kubernetes Pod

· #kubernetes #shell

TL;DR

A workaround for putting files in a Kubernetes Pod.

If you want to put a file in a Kubernetes Pod, the way to go is usually the command kubectl cp ....

Alas, this requires that the target Pod has tar installed. Which… might not always be the case.

IF the target Pod has a working shell, though, you can use the program below, like this:

kube-put /path/to/local/file /path/inside/pod/file <kubectl exec params>

where <kubectl exec params> will be the parameters you would normally use to execute something in the target Pod/container, e.g. setting the namespace with option -n, providing the name of the Pod and optionally providing the name of the target container with option -c. Example:

kube-put $(which kube-put) /tmp/kube-put \
    -n my-namespace pod/my-pod-name -c my-pod-container-name

Here is the program (local version here):

kube-put 2.75 KiB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 
#!/bin/sh

quote () { printf %s\\n "$1" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/'/" ; }

shell_wrap() {
   local source="$1"
   local target="$(quote "$2")"

   # we might want to avoid auto-detection of base64 in the remote system
   if [ "$USE_EMBEDDED_BASE64" = '1' ] ; then
      printf '%s\n' 'base64d() { base64_d ; }'
   else
      cat <<'END'
base64d() {
   if type -f base64 >/dev/null 2>&1 ; then
      base64 -d
   else
      base64_d
   fi
}
END
   fi

   # main part of reote script
   cat <<'END'
base64_d() {
   tr -d '\n' \
   | while true ; do
      line="$(dd bs=64 count=1 2>/dev/null)"
      [ -n "$line" ] || break
      printf %s\\n "$line"
     done \
   | sed -e 's_A==_@@_;    s_Q==_@,_;    s_g==_,@_;    s_w==_,,_;
             s_A=_@@@@_;   s_E=_@@@,_;   s_I=_@@,@_;   s_M=_@@,,_;
             s_Q=_@,@@_;   s_U=_@,@,_;   s_Y=_@,,@_;   s_c=_@,,,_;
             s_g=_,@@@_;   s_k=_,@@,_;   s_o=_,@,@_;   s_s=_,@,,_;
             s_w=_,,@@_;   s_@=_,,@,_;   s_4=_,,,@_;   s_8=_,,,,_;
             s_A_@@@@@@_g; s_B_@@@@@,_g; s_C_@@@@,@_g; s_D_@@@@,,_g;
             s_E_@@@,@@_g; s_F_@@@,@,_g; s_G_@@@,,@_g; s_H_@@@,,,_g;
             s_I_@@,@@@_g; s_J_@@,@@,_g; s_K_@@,@,@_g; s_L_@@,@,,_g;
             s_M_@@,,@@_g; s_N_@@,,@,_g; s_O_@@,,,@_g; s_P_@@,,,,_g;
             s_Q_@,@@@@_g; s_R_@,@@@,_g; s_S_@,@@,@_g; s_T_@,@@,,_g;
             s_U_@,@,@@_g; s_V_@,@,@,_g; s_W_@,@,,@_g; s_X_@,@,,,_g;
             s_Y_@,,@@@_g; s_Z_@,,@@,_g; s_a_@,,@,@_g; s_b_@,,@,,_g;
             s_c_@,,,@@_g; s_d_@,,,@,_g; s_e_@,,,,@_g; s_f_@,,,,,_g;
             s_g_,@@@@@_g; s_h_,@@@@,_g; s_i_,@@@,@_g; s_j_,@@@,,_g;
             s_k_,@@,@@_g; s_l_,@@,@,_g; s_m_,@@,,@_g; s_n_,@@,,,_g;
             s_o_,@,@@@_g; s_p_,@,@@,_g; s_q_,@,@,@_g; s_r_,@,@,,_g;
             s_s_,@,,@@_g; s_t_,@,,@,_g; s_u_,@,,,@_g; s_v_,@,,,,_g;
             s_w_,,@@@@_g; s_x_,,@@@,_g; s_y_,,@@,@_g; s_z_,,@@,,_g;
             s_0_,,@,@@_g; s_1_,,@,@,_g; s_2_,,@,,@_g; s_3_,,@,,,_g;
             s_4_,,,@@@_g; s_5_,,,@@,_g; s_6_,,,@,@_g; s_7_,,,@,,_g;
             s_8_,,,,@@_g; s_9_,,,,@,_g; s_+_,,,,,@_g; s_/_,,,,,,_g;' \
   | sed -e 's/\([,@]\{4\}\)/\1 /g' \
   | sed -e 's/@@@@/0/g; s/@@@,/1/g; s/@@,@/2/g; s/@@,,/3/g;
             s/@,@@/4/g; s/@,@,/5/g; s/@,,@/6/g; s/@,,,/7/g;
             s/,@@@/8/g; s/,@@,/9/g; s/,@,@/a/g; s/,@,,/b/g;
             s/,,@@/c/g; s/,,@,/d/g; s/,,,@/e/g; s/,,,,/f/g;' \
   | tr -d ' ' \
   | sed -e 's/\(..\)/\\0x\1 /g' \
   | while read line ; do printf %b $(printf \\\\%04o $line) ; done
}
END

   printf 'base64d > %s <<"END"\n' "$target"
   base64 "$source"
   printf 'END\n'
   printf 'chmod %s %s\n' "$(stat -c %a "$source")" "$target"
}

main() {
   local source="$1"
   local target="$2"
   shift 2
   shell_wrap "$source" "$target" \
   | kubectl exec -i "$@" -- /bin/sh
}

main "$@"

You MUST specify the target filename, putting the target directory is not sufficient. You are welcome to provide patches 😄

The program tries to auto-detect if base64 is installed in the target system and, if not, use a (slow) shell-based alternative (you might have recognized the code from A POSIX shell-only Base64 decoder). You can force the use of the shell-base alternative by setting environment variable USE_EMBEDDED_BASE64 to value 1 (any other value will be ignored).

Happy transferring!

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