Attach to a container

POST /containers/(id)/attach

Attach to the container id

Example request:

POST /containers/16253994b7c4/attach?logs=1&stream=0&stdout=1 HTTP/1.1

Example response:

Content-Type: application/vnd.docker.raw-stream
Connection: Upgrade
Upgrade: tcp

{{ STREAM }}

Query Parameters:

  • detachKeys – Override the key sequence for detaching a container.
  • logs – 1/True/true or 0/False/false, return logs. Default false.
  • stream – 1/True/true or 0/False/false, return stream. Default false.
  • stdin – 1/True/true or 0/False/false, if stream=true, attach to stdin. Default false.
  • stdout – 1/True/true or 0/False/false, if logs=true, return stdout log, if stream=true, attach to stdout. Default false.
  • stderr – 1/True/true or 0/False/false, if logs=true, return stderr log, if stream=true, attach to stderr. Default false.

Status Codes:

  • 101 – no error, hints proxy about hijacking
  • 200 – no error, no upgrade header found
  • 400 – bad parameter
  • 404 – no such container
  • 500 – server error

    Stream details:

    When using the TTY setting is enabled in POST /containers/create , the stream is the raw data from the process PTY and client's stdin. When the TTY is disabled, then the stream is multiplexed to separate stdout and stderr.

    The format is a Header and a Payload (frame).


    The header contains the information which the stream writes (stdout or stderr). It also contains the size of the associated frame encoded in the last four bytes (uint32).

    It is encoded on the first eight bytes like this:

    header := [8]byte{STREAM_TYPE, 0, 0, 0, SIZE1, SIZE2, SIZE3, SIZE4}

    STREAM_TYPE can be:

  • 0: stdin (is written on stdout)

  • 1: stdout
  • 2: stderr

    SIZE1, SIZE2, SIZE3, SIZE4 are the four bytes of the uint32 size encoded as big endian.


    The payload is the raw stream.


    The simplest way to implement the Attach protocol is the following:

    1. Read eight bytes.
    2. Choose stdout or stderr depending on the first byte.
    3. Extract the frame size from the last four bytes.
    4. Read the extracted size and output it on the correct output.
    5. Goto 1.