Ansible Copy Module: Remote_src Issue Explained

Dec 1, 2025 by Alex Johnson 48 views

Ansible Copy Module: Unveiling the `remote_src` Conundrum

The Ansible copy module is a powerful tool for transferring files between hosts in your infrastructure. However, a reported issue highlights a potential misunderstanding or bug regarding the remote_src option. This article delves into the details of this issue, exploring the reported behavior and providing a comprehensive explanation of the situation.

Understanding the Reported Issue with `remote_src`

The core of the issue revolves around the expectation that setting remote_src: yes in the copy module would instruct Ansible to copy files from the source path on the target node to the destination path, also on the target node. In essence, this would be a server-side copy operation, eliminating the need to transfer the file to the control node first. However, observations and code analysis suggest that this might not be the case.

The user reporting the issue noticed that even with remote_src: yes, the Ansible copy module seems to require the source file to exist on the control node. Furthermore, the checksum calculation, which is used to determine if a file needs to be copied, appears to be performed locally on the control node rather than remotely on the target. This behavior contradicts the expected functionality of remote_src and raises questions about its intended use.

The snippet of Ansible code that triggered this observation is part of a larger task aimed at setting up PXE (Preboot Execution Environment) and EFI (Extensible Firmware Interface) loaders. The task involves copying several files from specific locations to the TFTP (Trivial File Transfer Protocol) root directory on the target server. The with_items loop iterates through a list of dictionaries, each specifying the source and destination paths for a file.

- name: COPY | setup pxe and efi loaders
  copy:
    src: "{{ item.src }}"
    dest: "{{ linux_installation_server_tftp_root }}/{{ item.dest }}"
    remote_src: yes
    mode: "0644"
    owner: root
    group: root
  with_items:
    - src: /usr/lib/grub/x86_64-efi-signed/grubnetx64.efi.signed
      dest: EFI/debian/grubx64.efi
    - src: /usr/lib/shim/shimx64.efi.signed
      dest: EFI/debian/shimx64.efi
    - src: /usr/lib/PXELINUX/pxelinux.0
      dest: pxe/pxelinux.0
    - src: /usr/lib/syslinux/modules/bios/menu.c32
      dest: pxe/menu.c32
    - src: /usr/lib/syslinux/modules/bios/ldlinux.c32
      dest: pxe/ldlinux.c32
    - src: /usr/lib/syslinux/modules/bios/libutil.c32
      dest: pxe/libutil.c32
    - src: "{{ linux_installation_server_tftp_root }}/oraclelinux/8/BOOTX64.EFI"
      dest: EFI/oraclelinux/shimx64.efi
    - src: "{{ linux_installation_server_tftp_root }}/oraclelinux/8/grubx64.efi"
      dest: EFI/oraclelinux/grubx64.efi
    - src: "{{ linux_installation_server_tftp_root }}/oraclelinux/9/BOOTX64.EFI"
      dest: EFI/oraclelinux/shimx64.efi
    - src: "{{ linux_installation_server_tftp_root }}/oraclelinux/9/grubx64.efi"
      dest: EFI/oraclelinux/grubx64.efi

The expectation was that with remote_src: yes, Ansible would copy these files directly from the target server's filesystem to the specified destination, without involving the control node in the file transfer. However, the observed behavior and the analysis of the copy module's source code suggest a different reality.

Diving into the Code: Why the Confusion?

To understand the discrepancy between the expected and actual behavior, it's crucial to examine the relevant code snippets from the Ansible copy module. The user reporting the issue highlighted two key sections of the code that contribute to the confusion.

The first section involves the initial checks performed on the source file:

    src = module.params['src']
    b_src = to_bytes(src, errors='surrogate_or_strict')
[...]
    remote_src = module.params['remote_src']
    checksum = module.params['checksum']

    if not os.path.exists(b_src):
        module.fail_json(msg="Source %s not found" % (src))
    if not os.access(b_src, os.R_OK):
        module.fail_json(msg="Source %s not readable" % (src))

This code snippet reveals that even when remote_src is set to yes, the module checks for the existence and readability of the source file (b_src) on the control node, not the target node. This is a critical point because it directly contradicts the expected behavior of remote_src. If the source file doesn't exist or isn't readable on the control node, the task will fail, regardless of whether the file exists on the target node.

The second point of concern is the checksum calculation. The user noted that the checksum is always calculated locally on the control node. This means that Ansible is comparing the checksum of the local file (on the control node) with the checksum of the destination file (on the target node) to determine if a copy is necessary. This approach further reinforces the idea that remote_src doesn't fully function as a server-side copy mechanism.

The limited usage of remote_src within the module's code further supports the observation that its functionality might be incomplete or not fully implemented as intended. A search for remote_src in the module's source code reveals that it's not extensively used, suggesting that its impact on the overall file copying process is limited.

Implications and Potential Workarounds

The observed behavior of the remote_src option has significant implications for Ansible users who rely on it for server-side file copies. It means that files intended to be copied between target nodes must also be present on the control node, which can be inefficient and impractical in many scenarios.

For instance, consider a situation where you need to copy a large file between two remote servers. If remote_src were working as expected, Ansible would simply instruct the target servers to transfer the file directly, without involving the control node. However, with the current behavior, the control node would need to download the file from the source server and then upload it to the destination server, effectively doubling the network traffic and increasing the overall execution time.

So, what are the potential workarounds for this issue? Until the behavior of remote_src is clarified or fixed, users can employ alternative approaches to achieve server-side file copies.

One common workaround is to use the command or shell module to execute a command like cp or rsync directly on the target node. This allows for a true server-side copy operation, bypassing the limitations of the copy module's remote_src option. However, this approach requires careful handling of command syntax and potential security implications.

Another alternative is to use the synchronize module, which is based on rsync. The synchronize module offers more advanced features for file synchronization, including the ability to perform server-side copies. It's generally considered a more robust and flexible solution compared to the copy module with remote_src for complex file transfer scenarios.

The Importance of Clear Documentation and Communication

The confusion surrounding the remote_src option highlights the importance of clear and accurate documentation. If the intended behavior of remote_src is not a true server-side copy, the documentation should explicitly state this limitation. This would prevent users from making incorrect assumptions and avoid potential frustrations.

Furthermore, open communication between Ansible developers and the user community is crucial for addressing such issues. Bug reports and discussions like the one mentioned in this article provide valuable feedback for improving Ansible's functionality and usability.

Conclusion: Understanding the Nuances of `remote_src`

In conclusion, the remote_src option in Ansible's copy module appears to have limitations that might not be immediately obvious. While it might seem like a straightforward way to perform server-side file copies, the observed behavior and code analysis suggest that it doesn't fully function as such. The requirement for the source file to exist on the control node and the local checksum calculation contradict the expected functionality of a true server-side copy mechanism.

Until this behavior is clarified or addressed, users should be aware of these limitations and consider alternative approaches like the command, shell, or synchronize modules for achieving server-side file transfers. Clear documentation and open communication within the Ansible community are essential for resolving such issues and ensuring that users have a clear understanding of Ansible's capabilities.

For more information on Ansible and its modules, you can refer to the official Ansible documentation: https://docs.ansible.com/